I think some people use symlinks or sync software/rsync to keep the settings folders mirrored. If you search the forum a few things will probably show up.
I have two main vaults that I use for two completely different things, so want the theme, workspace, plugins, etc, to be different between the two.
I’ll also add that for me anyway, having a different theme, etc., for my two main vaults keeps my brain focused on what I’m doing at the moment. It also makes it easy to avoid typing in the wrong vault!
Not that you are asking this, but I see lots of questions here and on Discord about how to deal with vaults. Everyone will have different use cases, of course, but I think most people tend to settle on one or two vaults over time instead of having separate vaults for project1, project2, gardening, etc. Work and not-work seem to be the big ones.