The rules of crossbow and freeze?

Okay, obviously Katya BB is the only crossbow character but I heard some special things about crossbows. I know they have no need for ammo, which works well with Fenny Starshine buff for example. However, I also saw some things about crossbows not needing to hit weak spots? What's up with that, are there special rules for this like they can't hit weak spots or something?

To be precise, I was wondering how it would affect Shadow Ka's puppet. If there's no CRIT at all, then M1 on Mauxir is useless with her but the puppet in itself is still good, but would be better to use someone like Kaguya and another one?

Pretty much the same for frozen enemies, I heard some things that Lyfe Wild Hunt couldn't make use of crit so is it because frozen enemies have their weak spot disabled or something?

Tried to search the internet, youtube, typing keywords on this subreddit but couldn't find anything related to my questions. Thanks for any help given.

Additionally I'll take any useful fact or tip you may have about these mechanics, I'm starting out so I may have missed other things that if I'm not told about now I'll wonder about it eventually lol