First off, NATO isn't claiming to be fighting this war yet, so dictating terms of winning isn't up to them. Obviously NATO has a vested interest in seeing Ukraine absolutely decimate Russia's military so that they don't have to and they're willing to send old weaponry (While replacing with new) to allow that to happen. I don't think there's any need for NATO to currently make any statement as to what defines victory other than they support Ukraine in their fight. It's up to individual countries to determine when they think enough has been spent on their end, and countries may start lobbying for Ukraine to make concessions later on; especially if Russia comes forward with a peace deal that says we leave, we're sorry, just let us keep Crimea and we'll leave you be and even pay to rebuild. Now I doubt Russia will ever do that, but who knows. It's way too early to set goalposts and cement them in place because things change quickly.
I'm sure that if NATO thinks that Ukraine can kick Russia out of Crimea then they'll happily support that, I think if it appears impossible, then maybe they'll silently start taking backchannels to push Ukraine to make concessions and allow Ukraine to make the "decision" while they continue to "support" Ukraine.
Now the minute that NATO puts their troops into the battle and physically starts fighting Russia, then they get to set the terms. Until then it's ridiculous to demand that they do. I think it's pretty clear that they'd love to see Ukraine take back all of their borders and completely remove Russia from all of it. It's not yet certain whether that's possible. They're not going to stab Ukraine in the back and say it isn't, because we simply don't know.
Now obviously (Unless Russia does something insane like go Nuclear) I don't see NATO supporting any major incursion into Russia. (That's obviously different from striking supply lines that are being used to invade and strike Ukraine). But for now, they'll support Ukraine as long as it makes sense to do so. If that means all the way to pre-2014 borders then they'll do that, if it appears that they need to accept something less then they'll probably do that. But to make any bold claims as to what "winning" is doesn't do any good for anybody. Let Ukraine make those claims and adjust as the war plays out.