Many flathub apps and flatpaks apps in general need later flatpak version as current one in RHEL 8 is alot old. It refuses to install many flatpak applications and flathub applications here is an example of openh264 required codec by many flathub applications -

[SHuRiKeN@JatinPC ~]$ flatpak update
Looking for updates...
Installing in system:
org.freedesktop.Platform.openh264/x86_64/19.08 flathub 8801c9a82f9c
Is this ok [y/n]: y
Installing: org.freedesktop.Platform.openh264/x86_64/19.08 from flathub
Warning: Failed to install org.freedesktop.Platform.openh264/x86_64/19.08: runtime/org.freedesktop.Platform.openh264/x86_64/19.08 needs a later flatpak version (1.4.2;1.2.5;1.0.9;)
[SHuRiKeN@JatinPC ~]$ 

Most of the applications are unable to even install because many flatpak packages need later flatpak version.