I don't know if they posted to a community on an instance not federation with Lemmygrad but I don't see another post from their profile. But no, it's fine to post to different communities. That's also why cross-posting exists
Corporate app frontends track everything you do and see. They can record your mouse movement and watch it again, they track your scrolls, every button click, and even sometimes what you type in inputs even when you don't actually save them (like an Instagram comment you decide not to post, or a video search you don't actually search). There is a lot of tracking done on the frontend. Some of it could also be done in the backend (and a part of that is), some not
I don't have any answer for the point where you would not trust Google even for the hardware (even though I don't think there is any risk on the current devices)
But concerning the "don't want to support Google" an easier answer is to buy a second-hand Pixel
What do you need to do to je a fascist? Killing millions of people in the middle east, africa, south America and Asia because they have a more brown skin (except for one of the them) and same internally is not enough apparently, as well as passing fascists laws
I don't know if they posted to a community on an instance not federation with Lemmygrad but I don't see another post from their profile. But no, it's fine to post to different communities. That's also why cross-posting exists