You can get a climbing hangboard and hang it over a doorway. Do a pyramid training (2, 4, 6, 8, 6, 4, 2s with 5s pause in between) and your fingers and wrists will get much stronger

I use a Beastmaker 1000 hangboard and follow the Emil's Sub-max Daily Fingerboard Routine on the app Crimpd each day. Absolutely amazing results within a month. I really suggest everyone gives it a try.

If you're just hanging the exercise/stretch is often called a dead hang

You can also do it in the gym, if they have one of the "machines" shown at the very right in this picture: https://www.fit-star.de/Resources/Public/Content/Specials/He... - not sure how they're called or how common they are, but you put your lower arms on the armrests, grab the handles, rest your back against the blue ball and just let your legs hang. Then you can do some ab exercises.

That's just nature's incentive to keep up your grip strength