I recently tried to start up some new accounts across all of big tech, while keeping my true identity private. I was making up names etc. I wanted to try out the services under a fresh new name and see what it was like (Facebook feeds etc).
Every one of them required a phone number and had all kinds of algos and databases in place to thwart anonymity. If all of your demographic information didn't match the country your IP address was in the experience turned into a brick wall.
I did this a few years ago when establishing an onion (new accounts created and accessed only over VPN+TOR) identity for the dark web and didn't have a problem.
If I needed to hide my identity and communicate with people as a non-techie journalist or dissident I would not know how to proceed at this point.
This is not being done to fight terrorism. The real reason is to ensure that every user is a real person that can be sold.
When some fat cat spend thrift advertising executive complains about possible sock puppets numbering in the millions on their platform they just kick back and explain thier byzantine system of identity verification.