This could have been the case, but Discord blocks me from making new accounts without a separate, expensive mobile phone number.

You can’t even join most servers without having a bot ping your name publicly. This name is then searchable by any user in that server by searching for “mentions:yourcurrentname#tag”. This applies even if you changed your username since then.

You also cannot turn off the ability for someone to see what mutual servers or mutual friends you have.

Any of the above issues would be manageable as a single issue, but when combined, Discord is the worst tool for privacy, bar none.