Proton

Assuming ProtonMail supports catch-all (I don't use Proton), this is fine and a typical use of the catch-all. You may get weird looks when you give a business their name back as your email, and if anyone figures out that you have a catch-all they might just spam you regardless, at any email address they want, e.g. "icanfreelyspamyou@catata.fish". I would add a string of numbers/letters at the end, like "target.akr8@catata.fish" so you can be sure when someone sells your email.

All said, it's a little bit weak to any determined adversary. Any human who figures out your plan can easily start playing around with it - Target may sell your email as "thisguywantsspam@catata.fish" and you'll never know who sold it.

This is exactly how I use it. Basically, if you receive spam on webshop@catata.fish you know exactly who sold/"lost" your address.

One downside is that you cannot send from this address, but you usually don't need that anyway. And in the rare case that you do, you can just create an actual alias.

Don't use + as delimiter. It is an email standard for alias and will send the email to the none alias version inbox. Better to use a different delimiter, like minus, -, instead. Not sure how easy it is to do with Proton.

I keep a whitelist of email addresses allowed, the rest is therefore blocked. This means I can't send to random@example.com and get to the inbox.