Some people have been able to follow me (for example Patrick).

On the other hand, when I try to register to some crossposting services (between FediVerse and Twitter), they are not able to recognize my handle. So, maybe it is a client or library problem.

Which client are you using? Can you try some other clients?

A list of available clients is here: https://joinmastodon.org/apps

Merry Christmas!

Dashamir