...
The feature is called
plus addressing,
subaddressing or
tagging and I use that with Gmail, Proton Mail and Posteo accounts. There are sometimes restrictions with sending emails from such
subaddressing email addresses, depending on the particular email provider.
A quick Google search gives me the following list of major
[1] mail providers that claims they support this feature (I haven't verified it for most of them, especially those which I don't personally use myself):
Gmail, outlook.com, Microsoft 365 (Exchange Online), Proton Mail, Fastmail, iCloud (Apple), Yahoo Mail, mailbox.org, posteo.de, mail.de, mail.com
For a self-hosted mail server, I know from first-hand experience that Mailcow does support it, too.
Some (stupid) services don't allow a '+' in the email address you try to register with which in my opinion is a violation to valid email address rules. But what can you do if their stupid email address parsers hiccup...
...
From a privacy viewpoint you're right but to my knowledge the lower tiers of Proton Mail only have a very limited number of usable privacy friendly email aliases (only 10). You need a quite high tier to have an unlimited number of aliases, IIRC.
[1] The list is likely non-exhaustive and is what the Google search AI spit out when I aimed to get a quick overview. Take it with the necessary grains of salt.