Just to check, does the Insert (Ins) key add a new paint layer? You may have to wait until it’s stopped adding new layers to try that.
For your XP-Pen tablet, check with the XP-Pen website to see if you have the latest driver installed. If you haven’t, uninstall the current driver, restart your PC then download and install the latest driver, following any detailed instructions in the manual, then restart your PC.
In your XP-Pen setup utility, have you created an application profile for krita?
If you have, delete it, close the utility, then open it again and create a new application profile for krita while krita is running. Close the utility then try again.
If you haven’t created an application profile for krita then you should create one, as described above.
Does that fix the problem?
If not, enable the Log Viewer with Settings → Dockers, enable Log Viewer.
At the bottom of the Log Viewer docker are some icons. Hover your cursor over them to see the tooltip for what they do. (You may need to use a mouse for that unless you have very steady hands.)
Using the ‘Configure Logging’ icon, enable all types of logging.
Then press the Clear The Log icon and wait for a few new layers to be made.
You can’t do copy/paste from the Log Viewer so click the Save The Log icon to save it as a .log (text) file.
Then copy paste a few lines from the end of the log to a reply here.