I don't get how you can compare Sinner's UTR against Sabalenka's when they're based to two disparate group scores? Doesn't there need to be at least a modicum of cross-pollination to make a meaningful comparison?
There is some cross pollination. Women can play vs men, just usually don't. I'm fairly certain singles UTR is universal across players, it only distinguishes between doubles and singles UTR.
UTR can also include unranked games if one of the players submits a score and the other approves it.
UTR can also include unranked games if one of the players submits a score and the other approves it.