Only thing I can find on requesting to take over an inactive account is here:

> We do not accept requests to release, transfer, or reclaim usernames on the basis that they appear inactive or unused. If the username you want has already been claimed, you will need to select a different available name unless you are submitting a trademark complaint as described below.

https://docs.github.com/en/site-policy/other-site-policies/g...

Also even the original user renames or deletes their account any popular repos they have will get tombstoned, so the new owner can't recreate them:

> GitHub uses a tombstoning algorithm to reduce the risk of repo-jacking by permanently retiring specific owner name, repository name combinations. The github/cmark-gfm example above is purely hypothetical, because, in that scenario, the old name would get automatically tombstoned. For example, even if an attacker managed to register the username github, they would still be prevented from creating a new repository with the name cmark-gfm because that owner name, repository name combination (github/cmark-gfm) would be permanently retired. Therefore, repo-jacking is only a risk for repositories that fall below a certain usage threshold. We don’t tombstone all renamed repositories because there’s a tradeoff between usability and security: a tombstone is a potential inconvenience for our users which we don’t want to impose unless there’s a genuine security-related reason to do so. That’s why our tombstoning policy only kicks in after the repository has met certain criteria, such as exceeding a specific number of clones.

https://github.blog/security/supply-chain-security/how-to-st...