They could be talking the promises not to expand NATO. There was no treaty or formal agreement signed, just some verbal claims made in private, and they broke down almost immediately when Russia collapsed much further than it initially appeared it was going to and now fully-independent countries like Estonia, Latvia, and Lithuanian desperately begged to be let back into NATO under fears that Russia would attempt to invade and retake control when they regained strength.
They could also be talking about the Minsk Agreement, with was a 2014 cease-fire between Ukraine and the Russia-backed Donbas separatists. That agreement was repeatedly violated by both sides almost immediately, violated most seriously by the pro-Russian forces in the battle of Donetsk Airport, and was always tenuous because Putin repeatedly claimed he wasn't bound by the agreement.
Or they're talking about Minsk II, which was a 2015 attempt at a cease-fire that was never really implemented in the first place and fell apart for the same reasons Minsk I did.
No matter which of the three they're talking about its disingenuous as fukk, because the "don't expand NATO" shyt was never a treaty and has been ignored for 30 years, while the Minsk accords were only necessary in the first place because Russia was throwing its forces into eastern Ukraine and Russia has already violated them almost continuously.