Windows has also been doing that for some time now. Only Linux is relatively "clean" from that perspective, but even now some distros are beginning to sneak in spyware. The enshittification of OSes continues...
Citation needed. I remember Ubuntu sneaking in some stuff a couple of years ago[0], but most of the mainstream distros have a clean track record. What are you referring to exactly?
0: https://www.omgubuntu.co.uk/2018/02/ubuntu-data-collection-o...
Companies have tried buying floss software specifically to add spyware, such as audacity.
It’s not a big fraction of what proprietary OS does, but the threat grows steadily each year.