If you can see a flag in the system tray, click it to change to Danish keyboard.
If not, use the Set Session keyboard layout in Control Centre > Session to get back your dk keyboard momentarily and revert the /etc/default/keyboard configuration to your previous one and reboot.
I recommend you try a live session of antiX 19.3 to see if everything there works out of the box (including your keyboard). If it works properly, you may consider a complete reinstallation.
But first, I would create a system snapshot of your current antiX 16/17 system and then start experimenting again. At least with a snapshot you can restore your system to how it was before in case an experiment goes wrong.