Hmm, it didn’t used to require an email address but it appears that now matrix.org does. It may be a spam-fighting measure because they have had a lot of trouble with that in the past. …not that a email will do much.
You can try finding a different homeserver that doesn’t require an email address to sign up (or run your own if you are ambitious).
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I tried my server on a new android profile and the field was captioned “username or email” so I entered my username and I could proceed.
Did you try the web version of element on those servers?
Matrix and privacy 🤭
Here’s a list of other homeservers: https://tatsumoto-ren.github.io/blog/list-of-matrix-servers.html
An open network for secure, decentralized communication