Pretty much no social media platform will accept Protonmail as an address without also having a phone number.
Got banned from Discord within 3 hours, literally all I'd done was send three friend requests and join one discord. My IP was rotating and I then needed to have 2-factor authentication (and protonmail wasn't allowed, I needed that phone number).
So, I went out and bought a burner phone, cash, with a 1-year prepaid account. Got it setup over a wired proxy with all radios turned off. Now at least I had a Google account! (they also require a phone number)
And Discord proceeded to reject it, because I needed to have a 'real' phone number from a major carrier.
I essentially needed to craft an entirely new identity if I wanted to be truly anonymous. It was eye-opening how invasive and pervasive the 'track you down to a real identity' accounts have become.