AFAIK Season 3 is currently NOT available in UHD.
https://www.amazon.com/dp/B07GL8V632
"[Amazon's] agreements with the content provider don’t allow purchases of this title at this time."
Time will tell, but AFAIK there's not yet any news about that (see Dom834's reply below).
FWIW, they have a placeholder page for S3 4K, but not yet any proof that it'll be released. ("This title is currently unavailable ... agreements with the content provider don’t allow purchases of this title at this time.") :-/