Can't use .local domain for the hostname?

I’m a tiny bit confused. I tried using (hostname).local and it was rejected. I don’t remember the exact error.

I use conditional forwarders in active directory to typically send .local requests directly to my pihole.
Instead of using (hostname).local I was forced to use (hostname).(mydomain).localdomain

I just think that would be confusing for people, and it seems like .local addresses shouldn’t be prohibited. It makes it easier to setup DNS that way, otherwise I need to setup LOCAL dns records on 2 Active Directory machines AND on both of my piholes.

I see no problem to add a .local domain, either as web/maill domain or as hostname. It’s important to know what where you trying to do, how and the error you get.