If your IP (and possible your browser) looks “suspicious” or has been used by other users before, you need to add additional information for registration on gitlab.com, which includes your mobile phone number and possibly credit card information. Since it is not possible to contribute or even report issues on open source projects without doing so, I do not think any open source project should use this service until they change that.
Screenshot: https://i.ibb.co/XsfcfHf/gitlab.png
I last used it seriously like 7 or 8 years ago and it was fine. I put it on par with GitHub at the time. The ability to self host for free without too much trouble also really affected my position on it.
I haven’t really enjoyed the few times I’ve had to use it in the last couple of years, though.