Regarding downloading from other people’s libraries, I believe they need to allow you to do so. I have a library that was shared with me, but I can’t download anything from them, although I can save it “offline” via the Plex app. The unfortunate thing is that the offline function doesn’t not work very well at all, it works about 20% of the time for me on iOS and Android.
Same, right after Windows 10 nuked my network drivers via any automated update that happened while I wasn’t home