Paid subscription of Proton bundles SimpleLogin, an email aliasing service. So you can have your personal email with your surname, and when you want to sign up to some shady corpo site, you give them a randomly generated email address using SimpleLogin. All emails sent to that alias email will be automatically forwarded to your personal email. You can then disable the alias email anytime and stop receiving emails.

I have both, a personal domain with my name and also an anonymous generic domain. I use the anonymous one for 90+% of my online stuff, and use a random unique address for every service (you can set up a wildcard in proton, so *@domain.org lands in the same inbox). I would recommend that for two reasons: if you own your anonymous domain you can move your mailprovider anytime (as opposed to using some email masking service), using unique addresses for every service enables you to easily figure out which one leaked your address if you start getting spam. Just make sure to use a generic name for the domain and dont get an exotic TLD (just get a .com .org or something). Some of the non traditional TLDs may negatively impact your spam scores, and its easy to find a .com or .org when you can literally choose any domain name you want.

You can have your own custom email domain and for the use cases you want to be "anonymous" use simplelogin or addy.io on top of that.

If that were to happen, nothing is stopping users from exporting their emails elsewhere.