Thumbs can get overuse injuries:
https://getreuer.info/posts/keyboards/thumb-ergo/index.htmlI have used ergo keyboards with thumb clusters for several years now. After a while, even though switching to a split ergo keyboard alleviated wrist pains, I developed thumb discomfort.
In the end I solved it by only frequently using the resting key of each thumb (space and backspace). And using the other thumb keys for infrequent things. I use homerow mods to have all modifiers in the alpha block.
if you find one you like it's a massive difference in how much usage you can get out of your thumbs while typing
Until they start to hurt. It can take a few years (just like wrist pains). Be careful!