Happened to me also. I had registered my username in the first year Github started. Around 10 years later i discovered that someone else assumed my username through reaching out to their support. I was using Github still actively but hadn’t committed for quite some time in public. I was very pissed when i discovered. Support refused to change my name back instead giving me a coupon i never asked for. Whoever thought at Github this to be a good idea didn’t think through. It’s like the most retarded solution to a problem every social platform faces i’ve seen so far in how it is checked through.