Ubuntu isn’t necessarily backdoored, but they have made some questionable decisions that violate people’s privacy and ability to audit them. Specifically, years ago they added a “feature” which was on by default where your system search would also query amazon at the same time. Which was shitty and anti privacy obviously, so they took it out after community pushback. An ongoing problem though is with their own packaging format, snaps. The client side snap software is open source, but it only interacts with the official canonical snap repository which is entirely closed source on the backend. This opens up the possibility of back doors in snap and snap applications, as well as invasive analytics and other spying. Mint doesn’t include any of this shit so id say its safe and clean