Just because you were able to create 2 aliases for the same third party website doesn’t mean this rule doesn’t exist. It absolutely does, regardless of if you use Proton Pass or Simple Login aliases. Just because Proton hasn’t enforced it yet with you doesn’t mean they can’t nor that they won’t.
You’re not the first person to say they were able to create 2 aliases with the same website. Various people have also reported getting flagged by Proton after creating three, including myself. Those people probably reached out to Proton Support as I did. And guess what they told me? The rule is one alias per third party website. Doesn’t matter if some people get away with 2. That’s the rules.
I got a warning after creating 3. You would think that means the limit is 2. I asked Proton and they categorically said no. The limit is one alias per third party website.
Also, it is completely irrelevant if the aliases are from SL or Proton Pass. The ToS that Proton Support quoted and linked me were from Simple Login.
This is a direct quote from the warning I got from Proton after creating 3 aliases for the same website:
You have tried to register multiple times to ********, and this is against the terms of service of SimpleLogin. Please don’t do that anymore.
If you continue registering multiple accounts to a single service we will have to disable your account.