I’m no expert on this, but because of the large allocation and the expense of booking flights/hotel, I think it’s 50/50 that some tickets will get down to matchday Cityzens, may be with a purchase criteria. And don’t forget, UEFA also sell tickets in online open sales. They’re a bit of a lottery, but that’s how the guy that I bought from for Porto got his.
I’m more optimistic than pessimistic that the majority of City fans who can go, will be able to get a ticket.
And if you want to remove the risk of not getting a ticket, you can go hospitality;
https://uclf.hospitality.uefa.com/packages/