Tab islands. A very poor implementation of something many others have done correctly for a while. I mean tab groups. I have it turned off, but I might use tab groups if implemented correctly. Not a big issue to me.
A big issue to me:
That awful awful animation when switching workspaces. I know enough about programming to know a lot of work went into that, but who asked for it? What problem was it supposed to fix? Did someone think it just looked cool?
And it wouldn't be a big fix to make it a configurable option to turn off in settings.