Many MtG designers say that use of guns and advanced tech doesn’t really suit Magic and therefore have no place in it. Although there are some exceptions, the general rule stands. But is it simply disregarded when it comes to Universes Beyond? They, kinda, have lots and lots of stuff that doesn’t fit the spirit of “Magic”. Yet they exist.This is just my opinion, as an outside contractor.
I don’t think anyone in canon should have like, a Glock, but the comically large muskets from the Alaborn I don’t think were a big deal. I don’t want anyone holding say, a modern 9mm in Magic canon though.
Magic has been pushing into more advanced “magitech” with Kamigawa and even some more contemporary-looking tech in New Capenna, but I honestly think restricting firearms in Magic has led to some great creativity and unique visual styles with stuff like spell casting finger guns and violin blasters on Capenna.
As for Universes Beyond, it’s hard to say. I’m not deeply involved with it. 40k focused on their own comically large weapons or with lasers over ballistics much of the time, but it’s also an outside Magic IP. Rick Grimes and Lara Croft are the only characters so far shown with modern handguns, and they’re holstered in both pieces of art.
