esc key doesn't work, only fn + esc
If you know that your keyboard has got the correct country identification and ISO/Ansi setting, you might try "xev" in Terminal app.
After some moments it will open a small window left on top of your screen.
Just press "esc" once, then any letter, next press "fn" and "esc". Last: Cmd-dot to stop the output.
Depending on what your Terminal window tells you you might get some hint.

Another command in Terminal "xmodmap -pk" delivers a list of your keyboard's Keycodes and Keysym-values.
Maybe there is s.th. unusual shown there. You might post relevant output here.