Verified with versions:
nmstate-0.3.4-27.el8_3.noarch
NetworkManager-1.26.0-13.el8_3.x86_64
Basically on RHEL 8.3 it works like on RHEL 8.4, but on 8.3 we must set subordinate ports(such as veth) controlled by NM explicitly.
The issues on RHEL 8.4 also exist on 8.3: #bz1929946 #bz1928745 #bz1929132
There is a new issue for 8.3: if linux bridge has been created, cannot copy-mac-from a new added subordinate.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory (nmstate bug fix and enhancement update), and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHBA-2021:1084