Reading through now, but one immediate concern, the Exertion Focus section at no point ever communicates how much exertion you get. There's a bit later that talks about bonus exertion where you can infer it works like 5e monk's ki pool and is = class level. But it doesn't say that.
It needs to say how many you get.
There's no way to replenish exertion. As written, once you expend your exertion, you never get it back. Ever. This is probably not intended? A level 20 adept probably has 0 exertion because they spent the 1 point they got when they leveled up in a fight, and have better things to spend their Hit Die on then regaining 1d4 exertion to make their class features work. Or worse, they didn't take battle meditation, and can't regain exertion at all.
Especially since this version of the monk doesn't regain exertion/ki when combat starts, which means that the only way to get it back is battle meditation.
Is that intended?
Aside from that, I definitely agree with other comments that the Adept's abilities generally cost too much exertion- lots of two cost for cool things that aren't actually useful. The 1 turn mirror image spell for 2 exertion is particularly egregious- it should either cost 1, or cost 3 and actually just cast the full spell and last a minute.
Actually, given that you can't realistically replenish exertion, I feel like adepts should get like, a lot. If I have to ration out a potential maximum of 30 exertion across the duration of my entire adventuring career, I'm just never going to choose class features that expend it, because once it's gone it's gone forever.