Debian still has ads in Firefox like everyone else, and also privacy issues of various kinds and severities.
I can disable the Ubuntu terminal ad in seconds, whereas the last time I tried to install Debian I gave up after several hours of dealing with getting the correct proprietary firmware blobs, etc., that the Ubuntu installer mostly handles for me. But ultimately Ubuntu doesn't have as effortless of desktop hardware support for gaming laptops/PCs as Windows does.
I am willing to entertain the possibility that commercial OSs have advantages. But the claim was "no OS is immune from this", while only pointing at a specific subset of OSs to support that claim and ignoring a wide selection of options that very much do appear immune to ads infesting the experience.
Also, you must not have tried Debian very recently, since as of https://lists.debian.org/debian-devel-announce/2022/10/msg00... it also includes firmware by default.
Debian is a thing. Perhaps no commercial OS?