i made an extension that adds a bookmarks button to the toolbar to replace the original functionality of the sidebar button:

https://conceptualspace.net/open-bookmarks.crx

just double click it and follow the prompts in opera to install it (opera discontinued their extension store that's why you must manually download it)

on the extensions page, make sure to toggle "allow in private mode" for it to work.

PS: if you're concerned about what you may be installing, you can see the full source code by just renaming the .crx file to .zip and extracting the contents. hopefully others get some use from this. took me 2 minutes! cheers