The Apple TV app may play a download file at the downloaded resolution settings. You may need to re-download if you want a higher resolution than what you downloaded before. Downloads from Apple’s media Store are at 1080p max.
The streaming quality for non-downloaded media will be according to the other setting. Streaming in 4K is possible for screens and computers set to 3840×2160 or more, else a lower resolution source is used.
Some titles available from your region’s Store in 4K, some in 1080p, maybe some in 720p. ‘Ad Astra’ (2019) seems to be available in 4K in my country, but that might be different in some other countries and country-like regions. It depends on local representation for the supplying studios.

4K HDR HDMI output from or to HDMI 2.0 ports requires HDCP 2.2 or later compatibility, and would need no more than 60 Hz, YCbCr w/ Chroma 4:2:0 or 4:2:2 (not RGB or 4:4:4), as exceeding that would require more bandwidth than HDMI 2.0 offers. A full HDMI 2.1 chain could support almost 3× more HDMI bandwidth though.
4K SDR HDMI output from or to HDMI 2.0 ports stays under the bandwidth limits when configured for 60 Hz regardless of Chroma setting.
For persistent issues, please contact the Apple Support staff for further assistance.