This isn't a direct answer, because I agree it is difficult to move away from Github's familiarities amongst developers - so it doesn't necessarily solve the problem for a collaborative codebase involving a handful or more developers (complete with Issues, PRs, etc) but if you are working with a less technical/developer oriented team ie- regardless of org size it's just you or maybe one other teammate who are the only ones involved directly in code/PRs then you can fairly trivially roll your own issue tracker or wiki.

Particularly if your work and the employer/client/org is primarily based on a web project (extra points, you already are managing their auth) then you could simply add a new subdomain or route to your existing web project that serves said self-hosted issue tracker or wiki.

Of course these things can get into the weeds but I do think that given the dramatically reduced turnaround times for a competent dev to spin up and customize in-house/self-hosted solutions for basic things like issues and wikis the strategy is more relevant and prudent than ever.