Here is a simple workaround:
In terminal: sudo apt install gxkb. And run gxkb( ad it to autostrt if you want it to load with the system.
If someone do not like those flags - here is simple pgn images with "letters" :
(i used Purisa Bold 18 font in gimp to create them, so you can edit them with the letters you want)
Just place them in /usr/share/gxkb/flags with overwriting.
If you want to use black clour - you should erase "(black)" in the files names.
Hope it would be helfull for someone