RouterOS doesn't have anything for that. You can add static AAAA records, but you'd need to find some way how to update them.
Thanks for that context. Pity RouterOS doesn't provide a way to update AAAA records.
It was originally like that, IPv6 address was derived from MAC address, but I think it's not guaranteed anymore.
That's true; in fact, no clients on my network use a MAC-derived IPv6 address currently.
And even if you do solve that, the whole thing is problematic, it won't work well, unless all devices use only your router as DNS resolver, because it's the only one that knows these names. But it isn't always the case, something can have hardcoded external resolver (you can hijack connections to that), or even worse, encrypted DoH resolver (you can't do much with that).
I'm fine with relying on the local DNS resolver here; most clients on my network will get it via DHCP and the ones that don't are probably only connecting out to the Internet anyway.
It may be easier to just give up and if all your devices support it, use mDNS with <hostname>.local, that's completely independent.
Ah, I do have mDNS working for at least some of my devices. It's at least a partial solution.