I think you're missing the point. This is a physical limitation. People don't write as much as they used to. I used to be able to write for hours, taking notes, writing papers, etc... Now, I try to take notes during a meeting and my hand cramps. And as a bonus, my handwriting never was great, but now it's illegible for me.
Yes, we all "could" re-learn this skill, but how many people will? If you asked me to type a paper on a locked-down computer, I could easily. If you asked me to write a 2000 word paper by hand in an hour, I doubt it would happen.
If we expect students to take in-person tests on paper, then you should also do the rest of the classwork on paper. I am completely in the camp that we learn more when we write something. The physical act is part of the learning process. But you can't expect students to write an in-depth exam without having the practice of doing it often.
Are you using a fountain pen, writing cursive and do you take care to hold it properly? Those three things fixed all my cramps
For righties.
I'm right-handed, but I had to learn left-handed cursive at school when I spent 5 months with a cast on my right hand.
If you did it before then, barring physical limitations which have occurred since then, you would struggle for a short while and then you would be fine. I also did coursework purely on paper, got out of practice, and then once my kids were in school got back into the habit of handwriting. I can even write cursive again. Cursive makes it much easier on the hand and wrist. There's a reason it was invented. :)