I have bought 3 used cars and gotten 2 teenagers thru permit and drivers test and license. Never had any appointments except for the driving test, and never had any long waits. All waits were much shorter than when I transferred my out of state license to CA in 2008 or 2009. Impressively well run bureaucracy, I'd say. And this with covid precautions to work around. Much better than the several east coast states I had prior experience with.

Now I do chose the office to visit with some care, and also (as an "elite WFH software engineer") time it so that the lines are likely to be shorter, so YMMV.

Can't be, in CA you can't return normal plates, they explicitly don't want them back. And you don't really have to return vanity plates either.

Rather, there's an online form for notifying them of a sale.

You definitely can return plates in California. They just don’t ask for them as a due course for any normal processes. But, you can choose to mail them in or turn them over to the clerk.