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
Does GitHub still only permit one account? I remember looking into it awhile back and not wanting to get things mixed up between personal/professional arrangements and the one account policy put me off.
congratulations then, it supports multiple accounts, haven’t used it yet though.