Github's scaling challenges have more to do with the write volume than the read volume. Even a project as big and active as Blender shouldn't make Gitea sweat too much on relatively modest hardware. Anonymous clones and such will surely be https, so, quite cache-friendly.

I wanna say Gitea has some config options for hosting static files (like releases) on s3-compatible storage then serving directly from there, so even that shouldn't be a problem. But I may be mis-remembering that part. And, again, a CDN or Varnish or whatever would be able to serve those files just as well from Gitea as from anywhere else.