It seems I did not try making a Lenovo account with the pm.me alias address. I did use a protonmail.com address when tried before swapping to making an account using a Tutanota address and attempting to replay the purchase sequence. I don’t remember the conversation I had with support when they deduced the error to protonmail addresses not being eligible for purchases for not “being verifiable” despite the fact that payment and billing information is also provided in a purchase. I don’t remember if the support technician claimed that the pm.me alias would also be blocked, but for some reason I never tried it.

There definitely are sites that block or restrict accounts using ProtonMail addresses. Obviously social media sites will be more likely to force an account to provide a phone number if one is using a proton mail address compared to for instance, a GMail address. There has been one site I have seen block/restrict ProtonMail outright, and that is Lenovo. It is not possible to actually make purchases from Lenovo directly if the account’s email is a ProtonMail address. Too be fair though, that is the only site I have seen any explicit account blocks/restrictions.