A tip is to host your own domain at an e-mail provider that allow you to receive e-mail for any recipient in a single mailbox (i.e. catch-all or wildcard), and use the following alias format when signing up at different websites or services:

<website>@<yourdomain.tld>

This allows you to filter incoming e-mail by which website/service you signed up for, regardless of what domain they send e-mail from (it can be different for account notifications vs newsletters etc.).

It will also help you detect if they have sold your contact details or had a data breach without announcing it publicly, since you wouldn't use that specific e-mail alias elsewhere.

Using your own domain name with catch-all enabled works fine, you just type whateveryouwant@yourdomain.com

My approach with companies that do this: Contact them, explain that I will not be giving them any money due to this aggressive anti-privacy practice, and take my business elsewhere.

Two things either don't use their service or you could get your own domain and then set up a catch-all so that you can create as many aliases as you want with your own domain. So like kroger@example.com, walmart@example.com, etc.

If you happen to be paying for iCloud storage, you could use their hide-my-email service for those rare accounts and have it send to your proton email (apple lets you use an external email to forward to). That's one of the big benefits of apple's alias solution; they are all in the icloud.com domain and no website would ever block that.

I discovered recently that github will flag your account for using a proton alias.

Some websites do that. They block at the domain level. It tends to become a escalating game of spinning up new alias domains.

https://proton.me/support/creating-aliases#additional

If you have a paid plan, you can create at least 10 additional addresses (depending on your plan) with any Proton domain (@proton.me, @protonmail.com, @pm.me, or @protonmail.ch) or a custom domain, if you have one.

I have a custom domain, which websites never block, because they have no way of knowing that I use it for aliases.

Lots of sites block mailinator.com domains, too.