Following the Y7S4 update (live on 6 Dec 2022 for Xbox One/X), there is a prompt to subscribe to Xbox LIVE Gold or Game Pass when the game connects to Rainbow Six Siege servers to query or update your squad status. This occurs when the game first loads, as well as when exiting a Training Grounds - Lone Wolf session. It may occur other times as well, but these are the only two I have encountered so far.
This is an EXTREMELY annoying pop-up! Please remove it!
I DO NOT subscribe to Gold or Game Pass and DO NOT need to, because I don't use any features that require them. In Rainbow Six Siege, specifically, all I play is Training Grounds - Lone Wolf, which does NOT require a subscription.
UPDATE: This issue also occurs with PlayStation 4 and a PlayStation Plus subscription.