I had this issue when I got my wife a “remarkable” tablet. Apparently the early gens were well known for getting the power button stuck and for being glued together and thus to disassemble.

I bought an iFixit kit and got it apart and the power button unstuck, but I never got the tablet back together.

The common suggestion for that particular tablet was to use a Dremel to widen the power button slot and liberate the button.