You can goto the URL opera://about, take note of the "profile" path, close Opera an delete the "Sessions" folder in the profile folder. It'll wipe out all your open tabs, but it might fix things.
If you need to save your open tabs, before doing that, in each workspace, right-click a tab, goto "save" and choose "all tabs to a speed dial folder". Then, rename the folder to the name of the workspace. Then, to get the tabs back, in each workspace, right-click on its corresponding speed dial folder and choose "open all in tabs".
You could also try deleting all your workspaces, restarting Opera and then recreating them. You can back up and restores your open tabs in them the same way as above if needed.
Another you can try is to click the 3 dots at the bottom of the sidebar and then hide some things (like some messengers) t see if it makes a difference. You can hide some workspaces and then unhide them. Stuff like that.