That's not really my use case, but seems like an important concern for many!

At that point, you probably want to use whatever features one of the big providers use, like: https://proton.me/support/aliases-mail

Maybe even something that'd sit in front of a mail server that you yourself control, I wonder what the variety of options out there is.

This is true for someone manually searching for your info, but sufficient to fool spam lists and most data brokers. This really depends on your threat scenario.