IIRC from the “What we left behind” documentary, they were shot on film. They even had a few minutes of HD material scanned from the film reels. It’s the CGI that was baked only into the tape version that makes it so difficult to do a HD remaster. And why they went back to the tapes when producing the DVD release.

They seem to have pulled Season 3 here in Germany even though it was marketed as an “Amazon Original”. Seasons 1 and 2 are still on Prime. Pretty disappointed because I just started a rewatch.