beeping when pressing keys usually means keyboard buffer full = software too slow to empty it in time. Why would XT-IDE bios cause that I dont know. hmm wrong IRQ set hijacking keyboard?

I tried all jumper settings for IRQ but without any changes.

Maybe I should write info about keyboard into autoexec.bat (UK, USA, doesn't mater only not german) but I forget how to do it.

I dont think that would make any difference. Imo it sounds like a hardware resource conflict.
you could start by revealing model of the mobo, have you tried different bioses for it?

Do you load the Keyb in your boot files? Maybe try to add a REM in front to disable it and see what happens...?
Is it the same DOS version as the boot disk?

So I am not loading any keyb files and I would like to do it but I don't remember how. It is so long time when I was doing it last time. I have to add some lines to autoexec.bat and config. sys for sure. Now I have to go to work for about 2 weeks but I will try all of Your propositions to solve this problem when I will be back to home.

So I have now original XT keyboard and it is working fine (no problem with XT-IDE). I used AT to XT keyboard adapter before so now I know that this adapter is a problem in this case.