LG is responaible for and pushes out the updates. T-Mobile can refuse to have their devices updated, but I can't see that happening. LG has always been incredibly slow when it comes to updates. Don't expect the Pie update until the end of June at the earliest.
LG's timeline for the V30 Pie update is the 2nd quarter of this year and I agree with syaoran that
it will be in June. Oreo was in May of 2018.