Same answer as "Facebook alternatives?" or "Twitter alternatives?" or "Photoshop alternatives?".
You have quite a few online git forges to choose from, like BitBucket, GitLab, sourcehut and certainly others but it all comes down to what you value in GitHub. If you value the social stuff, then no, there simply is no alternative. If you value the enterprise stuff, GitLab might check most of the boxes. If you don't care about the slick UI, the enterprise stuff, or the social stuff, then take a look at sourcehut. Etc.
You have quite a few online git forges to choose from, like BitBucket, GitLab, sourcehut and certainly others but it all comes down to what you value in GitHub. If you value the social stuff, then no, there simply is no alternative. If you value the enterprise stuff, GitLab might check most of the boxes. If you don't care about the slick UI, the enterprise stuff, or the social stuff, then take a look at sourcehut. Etc.