Description of problem:
Edited fontconfig by hand, but still valid. Attached below:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE fontconfig SYSTEM "../fonts.dtd">
<fontconfig>
  <!--
	THIS FILE WAS GENERATED BY libeasyfc 0.14.0
	DO NOT EDIT THIS DIRECTLY
	ANY CHANGES HAS BEEN MADE MANUALLY MAY BE LOST.
  -->
  <match target="pattern">
    <test name="lang">
      <!--lang=te-IN-->
      <string>te</string>
    </test>
    <test name="family">
      <string>Noto Sans Telugu</string>
    </test>
    <edit name="family" mode="append_last">
      <string>sans-serif</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="lang">
      <!--lang=te-IN-->
      <string>te</string>
    </test>
    <test name="family">
      <string>sans-serif</string>
    </test>
    <edit name="family" mode="prepend">
      <string>Noto Sans Telugu</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="lang">
      <!--lang=te-IN-->
      <string>te</string>
    </test>
    <test name="family">
      <string>Noto Serif Telugu</string>
    </test>
    <edit name="family" mode="append_last">
      <string>serif</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="lang">
      <!--lang=te-IN-->
      <string>te</string>
    </test>
    <test name="family">
      <string>serif</string>
    </test>
    <edit name="family" mode="prepend">
      <string>Noto Serif Telugu</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="family">
      <string>Noto Sans</string>
    </test>
    <edit name="family" mode="append_last">
      <string>sans-serif</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="family">
      <string>sans-serif</string>
    </test>
    <edit name="family" mode="prepend">
      <string>Noto Sans</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="family">
      <string>Noto Serif</string>
    </test>
    <edit name="family" mode="append_last">
      <string>serif</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="family">
      <string>serif</string>
    </test>
    <edit name="family" mode="prepend">
      <string>Noto Serif</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="family">
      <string>Cascadia Code PL</string>
    </test>
    <edit name="family" mode="append_last">
      <string>monospace</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="family">
      <string>monospace</string>
    </test>
    <edit name="family" mode="prepend">
      <string>Cascadia Code PL</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="family">
      <string>Noto Color Emoji</string>
    </test>
    <edit name="family" mode="append_last">
      <string>emoji</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="family">
      <string>emoji</string>
    </test>
    <edit name="family" mode="prepend">
      <string>Noto Color Emoji</string>
    </edit>
  </match>
  <match target="font">
    <test name="family">
      <string>Iosevka Fixed Slab</string>
    </test>
    <edit name="hinting" mode="assign">
      <bool>true</bool>
    </edit>
    <edit name="autohint" mode="assign">
      <bool>false</bool>
    </edit>
    <edit name="antialias" mode="assign">
      <bool>true</bool>
    </edit>
    <edit name="rgba" mode="assign">
      <const>rgb</const>
    </edit>
    <edit name="hintstyle" mode="assign">
      <const>hintfull</const>
    </edit>
    <edit name="fontfeatures" mode="append">
      <string>zero</string>
      <string>ss04</string>
    </edit>
  </match>
  <match target="font">
    <test name="family">
      <string>Cascadia Code PL</string>
    </test>
    <edit name="hinting" mode="assign">
      <bool>true</bool>
    </edit>
    <edit name="autohint" mode="assign">
      <bool>false</bool>
    </edit>
    <edit name="antialias" mode="assign">
      <bool>true</bool>
    </edit>
    <edit name="embeddedbitmap" mode="assign">
      <bool>false</bool>
    </edit>
    <edit name="rgba" mode="assign">
      <const>rgb</const>
    </edit>
    <edit name="hintstyle" mode="assign">
      <const>hintfull</const>
    </edit>
    <edit name="fontfeatures" mode="append">
      <string>calt</string>
      <string>ss19</string>
    </edit>
  </match>
  <match target="font">
    <test name="family">
      <string>Cascadia Code</string>
    </test>
    <edit name="hinting" mode="assign">
      <bool>true</bool>
    </edit>
    <edit name="autohint" mode="assign">
      <bool>false</bool>
    </edit>
    <edit name="antialias" mode="assign">
      <bool>true</bool>
    </edit>
    <edit name="rgba" mode="assign">
      <const>rgb</const>
    </edit>
    <edit name="hintstyle" mode="assign">
      <const>hintfull</const>
    </edit>
    <edit name="fontfeatures" mode="append">
      <string>ss19</string>
      <string>calt</string>
    </edit>
  </match>
  <match target="font">
    <test name="family">
      <string>Cascadia Mono PL</string>
    </test>
    <edit name="hinting" mode="assign">
      <bool>true</bool>
    </edit>
    <edit name="autohint" mode="assign">
      <bool>false</bool>
    </edit>
    <edit name="antialias" mode="assign">
      <bool>true</bool>
    </edit>
    <edit name="rgba" mode="assign">
      <const>rgb</const>
    </edit>
    <edit name="hintstyle" mode="assign">
      <const>hintfull</const>
    </edit>
    <edit name="fontfeatures" mode="append">
      <string>calt</string>
      <string>ss19</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="family">
      <string>monospace</string>
    </test>
    <edit name="family" mode="assign_replace" binding="strong">
      <string>Cascadia Mono PL</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="family">
      <string>ui-monospace</string>
    </test>
    <edit name="family" mode="assign" binding="same">
      <string>Iosevka Fixed Slab</string>
    </edit>
  </match>
  <match target="pattern">
    <test name="family">
      <string>Mallanna</string>
    </test>
    <edit name="family" mode="prepend_first" binding="strong">
      <string>Noto Sans Telugu Condensed</string>
      <string>Noto Sans Telugu UI</string>
    </edit>
  </match>
</fontconfig>

Version-Release number of selected component:
fonts-tweak-tool-0.4.6-3.fc38

Additional info:
reporter:       libreport-2.17.11
uid:            1000
runlevel:       N 5
kernel:         6.5.5-200.fc38.x86_64
type:           Python3
crash_function: __render_combobox
reason:         fonts-tweak-alias.py:267:__render_combobox:KeyError: 'ui-monospace'
executable:     /usr/bin/fonts-tweak-tool
interpreter:    python3-3.11.5-1.fc38.x86_64
cmdline:        /usr/bin/python3 /usr/bin/fonts-tweak-tool
package:        fonts-tweak-tool-0.4.6-3.fc38
exception_type: KeyError
cgroup:         0::/user.slice/user-1000.slice/user/app.slice/app-gnome-fonts\x2dtweak\x2dtool-27821.scope

Truncated backtrace:
fonts-tweak-alias.py:267:__render_combobox:KeyError: 'ui-monospace'

Traceback (most recent call last):
  File "/usr/lib64/python3.11/site-packages/fontstweak/main.py", line 60, in do_activate
    self.window = FontsTweakToolMainWindow(self, self.config)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.11/site-packages/fontstweak/main.py", line 95, in __init__
    hbox.pack_start(self._get_main_content(), True, True, 0)
                    ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.11/site-packages/fontstweak/main.py", line 136, in _get_main_content
    ui[u].set_config(self.config)
  File "/usr/lib64/python3.11/site-packages/fontstweak/tweaks.py", line 47, in set_config
    self.do_set_config()
  File "/usr/lib64/python3.11/site-packages/fontstweak/ui/fonts-tweak-alias.py", line 330, in do_set_config
    self.__render_combobox(l, an)
  File "/usr/lib64/python3.11/site-packages/fontstweak/ui/fonts-tweak-alias.py", line 267, in __render_combobox
    self.lists[alias].clear()
    ~~~~~~~~~~^^^^^^^
KeyError: 'ui-monospace'

Local variables in innermost frame:
self: <fonts-tweak-alias.FontsTweakAliasUI object at 0x7febe8c17180 (fontstweak+ui+fonts-tweak-alias+FontsTweakAliasUI at 0x55c1cff4cbb0)>
lang: ''
alias: 'ui-monospace'
kalias: 'ui-monospace'
flocalized: True