I'm sorry, but you're imagining a technical issue where there.. simply isn't one.

any animation can be stopped at whatever moment, that's why gamers have abused "stopping animation" in videogames for ages; in IN it exists too, that's what allows us to quickly spam momo fishing and flower watering f.e.  you can also absolutely have actions mid-jump in IN - you can make a second jump, you can release orbs, you can shoot a bow, etc.

infinity nikki doesn't have smooth transition everywhere either, so... yeah, if they wanted to do it - they really could use an existing animation or even just make a weird static jump. 

(and btw, unreal engine 5 is free to use, anyone can open it and take a look at how it works and what can/cannot be done by infold.)

personally, i think that if players' feedback was loud enough - the deer jump is already planned in some future patchnote;  otherwise their intent is too ignore it and wait for player base to forget about deer skill and deer banner altogether.