Issue with GitLab.com sign in
Attempting to sign in to GitLab.com using Tor Browser (13.0.14) results in a loop of anti-bot verification. However I do not believe this is an inherent block of Tor exit-nodes by Cloudflare itself. Because for instance the Cloudflare sign in has the same anti-bot verification that is completed successfully.
One potential factor might be that Tor Browser proxies Cloudflare challenges through an .onion service and either the configuration of Cloudflare or GitLab.com has a related issue.