I can use C-h m to check the bindings of my current major mode, if it’s one where I can rest my cursor. But how can I check the bindings that are present in, eg, isearch mode? I can set up such bindings, but I’m not sure how to review them.

Answer: describe-keymap

In emacs 28 there seems to be created the perfect function for this: (describe-keymap)¹

Footnotes

¹ Thanks to the answer on Reddit for this one: https://www.reddit.com/r/emacs/comments/q76kok/weekly_tips_tricks_c_thread/hguzylx/?context=3