alt Hacker NewsA split keyboard might still bring you some relief. Modifiers/enter/backspace/etc are usually moved away from your weakest fingers (pinkies) to your strongest (thumbs). I have Ctrl, Alt, backspace, delete, space, enter and shift all on my thumb clusters.
Here's an example of what that might look like: https://kinesis-ergo.com/wp-content/uploads/KB360-GBR_FRONT-... (though in the default configuration, shift is still on your pinky; you can customize this on most keyboards, or on OS level).
The rabbit hole goes very deep. Another option is home row mods: https://precondition.github.io/home-row-mods. A combination of thumb clusters and home row mods can reduce your finger strain a lot.
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I can't second Kinesis enough. I have been using them for 20 years now. I was starting to have issues and I haven't have a single issue with my hands or wrists since changing over. Also a good vertical mouse will help if you use a mouse much. I use trackballs or vertical mice interchangably.
Also the type of the key matters for tendonitis. Some have tactile feedback after the key is pressed but well above the bottom so you learn not to bottom out with force.
https://kinesis-ergo.com/products/#keyboards
(They used to have low-force options; perhaps all are low-force now?)