Stroke dude.
I had one and the biggest indicator was I couldn’t write but could do other things with my hand as it is mental not physical.
Are you able to speak normally?
The really bad news is you need to see a doc but it is too late for the meds that can “fix” it.
I seem to be fine in all other regards and the penmanship is getting better the more I try it.
My arm is still “TINGLY”
I tell ya it freaked me out when I couldn’t write.