User accounts are unavailable using a .local domain

There's no good answer.

The .local top-level domain means the same thing in all networks. In Microsoft Windows networks running Active Directory, that top-level domain was unfortunately used as an example domain, and more than a few folks decided to "squat" in that domain and not use a real and register a domain. That domain simply wasn't registered for this sort of use in years past, and now it's become part of an RFC for mDNS / Bonjour use.

If there was a reliable workaround for this network configuration error, then that would be widely available as many Microsoft Windows Active Directory sites have made this same configuration mistake. You can try shutting off Bonjour, but that'll probably introduce other issues.

In general, folks either deal with the errors and the flakies that arise here, or they register a domain and migrate to that registered domain or into a subdomain of that registered domain.

Migrating sooner rather than later is generally preferable, as networks do tend to grow and get more tangled.

I would not generally recommend trying to pick a bogus top-level domain. Given ICANN has started releasing a thousand or more new top-level domains (.guru, .bike, .plumbing, .kitchen, .land, .enterprises and some other new top-level domains just came online), "squatting" in an unregistered top-level domain — what .local used to be — is getting trickier, too.