Is there any way to see the parameters for a function even if it's just in loaded files? Using list_all_functions_all_buffers seems to do it but I can't find a way to back out of the command.

You just need to close the decls buffer like a regular buffer.

That said it's not the most practical way to get functions arguments. Have a look at Ryan Fleury's custom layer, I think there is a thing were it can display function arguments of the identifier under the cursor (not sure).

Works perfectly, though the layer has way more than I want so it will take me some time to strip all of that away.

If you're looking for something minimal, my modification might be of interest to you: https://gist.github.com/aolo2/aea5014a35031b0c915a7ad0948584b5

Example: 2021-10-13 10-55-42.mp4