Really? You can't conceive of any way that could make this work?
Because there are degrees of flight. Consider the 4e Pixie; it can fly, but it has a height limit of 5 feet, meaning it's more like a hover. Sorta like having a race that can cast fey step once per short rest--they can fly across a gap, but they can't fly up a wall or over a building.
And there are ways to get always-on flight through class or subclass, liked druid's wild shape or dragon sorcerer's wings, or a ring of flight.
And there are spells that grant flight pretty much whenever you might need it, especially once you're level 7+ and thus have plenty of spell slots of 3rd level or higher.
So...clearly PCs having sometimes-on flight isn't a problem, otherwise you'd be banning spells too. Clearly, PCs having (effectively) always-on flight at high level isn't a problem, otherwise you'd be banning Sorcerers. Clearly, PCs having limited or resource-costing flight isn't a problem, or you'd be banning Druids (or at least banning the ability to transform into songbirds etc.) Point being: it's not "the PC has access to flight, therefore it's intolerable." It's "the PC has too much access," or too easy access, or too early access, etc. Those things admit shades of grey, and thus provide extremely fruitful ground for seeking compromise. Example drafted in five seconds: maybe a race that grants 1/day feather fall at 1st level, and then 1/day levitate at a higher level, and finally 1/day fly at a higher level still, just as some Tieflings get a cantrip at 1st level, a 2nd level spell at level 3, and a 3rd level spell at level 5.
Even the "no evil PCs" thing--which is a hard line for me, in the sense of "I won't run a game for a PC that is genuinely, unequivocally, unrepentantly evil"--still admits a lot of leeway, a lot of possibility for finding mutually-acceptable solutions. I'm absolutely on board for a recovering evil person, someone hoping to achieve redemption or at least to compensate somewhat for the evil they did. I think it's wonderful to have a good PC who has one or two exploitable temptations that they can wobble about or even occasionally succumb to so long as they don't happily embrace it. I currently have a player's PC who is pretty hard neutral but pacifist, and thus is much more open to listening to villainous NPCs than most other characters. That's incredibly juicy, because it presents an opening for manipulative, desperate, or self-preserving antagonists to potentially get the PCs to let them get away with some of what they want, or to work with groups that other PCs would be too stuffy or do-goody to accept.
None of this requires that much creativity. It just requires that, even when you have a hard line, you think about what the hard line really requires. I say "I can't--and thus won't--run a game for unrepentant Evil PCs." The reason for that is, I not only don't enjoy doing the DM work to create interesting stakes, challenges, and rewards for unrepentant evil PCs...doing that would absolutely slowly sour my experience. Hence, things which avoid that slow souring are not a problem. If I'm still making interesting stakes, challenges, and rewards for either repentant or non-evil PCs, things are fine. So...it behooves me to look at those things.
The exact same process can be applied to what players want to do. Maybe they want to play evil because they think playing a good person is boring, which is...not generally the case in my game. Maybe they want to play someone who gets to break the rules--there's lots of ways to do that without unrepentant evil. Maybe what they really care about is nuance and depth, and that's something the two of us can work out a zillion different ways. Hence: both sides find the things they really truly can't budge on, and I find that pretty much always, there's room for some kind of compromise.
