The 2.2GB download is a 1280x720 50FPS MP4, definitely a long way from 4K HDR.

Testing with the --list formats option does not identify any higher resolution. Here is an example for the most recent episode:

tom@desktop:~$ youtube-dl --list-formats https://www.bbc.co.uk/iplayer/episode/b09hs07h/blue-planet-ii-series-1-6-coasts
[bbc.co.uk] b09hs07h: Downloading video page
[bbc.co.uk] b09hs07h: Downloading playlist JSON
[bbc.co.uk] b09hs074: Downloading media selection XML
[bbc.co.uk] b09hs074: Downloading m3u8 information
[info] Available formats for b09hs074:
format code extension resolution note
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_dash-audio_eng=128000 m4a audio only [en] DASH audio 128k , mp4a.40.2 (48000Hz)
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_dash_https-audio_eng=128000 m4a audio only [en] DASH audio 128k , mp4a.40.2 (48000Hz)
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_dash-audio_eng=128000 m4a audio only [en] DASH audio 128k , mp4a.40.2 (48000Hz)
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_dash_https-audio_eng=128000 m4a audio only [en] DASH audio 128k , mp4a.40.2 (48000Hz)
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_dash-video=827000 mp4 704x396 DASH video 827k , avc3.4D401E, 25fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_dash_https-video=827000 mp4 704x396 DASH video 827k , avc3.4D401E, 25fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_dash-video=827000 mp4 704x396 DASH video 827k , avc3.4D401E, 25fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_dash_https-video=827000 mp4 704x396 DASH video 827k , avc3.4D401E, 25fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_dash-video=1570000 mp4 704x396 DASH video 1570k , avc3.64001F, 50fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_dash_https-video=1570000 mp4 704x396 DASH video 1570k , avc3.64001F, 50fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_dash-video=1570000 mp4 704x396 DASH video 1570k , avc3.64001F, 50fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_dash_https-video=1570000 mp4 704x396 DASH video 1570k , avc3.64001F, 50fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_dash-video=2812000 mp4 960x540 DASH video 2812k , avc3.64001F, 50fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_dash_https-video=2812000 mp4 960x540 DASH video 2812k , avc3.64001F, 50fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_dash-video=2812000 mp4 960x540 DASH video 2812k , avc3.64001F, 50fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_dash_https-video=2812000 mp4 960x540 DASH video 2812k , avc3.64001F, 50fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_dash-video=5070000 mp4 1280x720 DASH video 5070k , avc3.640020, 50fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_dash_https-video=5070000 mp4 1280x720 DASH video 5070k , avc3.640020, 50fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_dash-video=5070000 mp4 1280x720 DASH video 5070k , avc3.640020, 50fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_dash_https-video=5070000 mp4 1280x720 DASH video 5070k , avc3.640020, 50fps, video only
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_hls-1013 mp4 704x396 1013k , avc1.4D401E@ 827k, 25.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_hls_https-1013 mp4 704x396 1013k , avc1.4D401E@ 827k, 25.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_bidi_uk_hls-1013 mp4 704x396 1013k , avc1.4D401E@ 827k, 25.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_bidi_uk_hls_https-1013 mp4 704x396 1013k , avc1.4D401E@ 827k, 25.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_hls-1013 mp4 704x396 1013k , avc1.4D401E@ 827k, 25.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_hls_https-1013 mp4 704x396 1013k , avc1.4D401E@ 827k, 25.0fps, mp4a.40.2@128k
iptv_streaming_1500_akamai_hls_open-1496 mp4 832x468 1496k , avc1.77.30, mp4a.40.2
iptv_streaming_1500_akamai_hls_open_https-1496 mp4 832x468 1496k , avc1.77.30, mp4a.40.2
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_hls-1800 mp4 704x396 1800k , avc1.64001F@1570k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_hls_https-1800 mp4 704x396 1800k , avc1.64001F@1570k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_bidi_uk_hls-1800 mp4 704x396 1800k , avc1.64001F@1570k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_bidi_uk_hls_https-1800 mp4 704x396 1800k , avc1.64001F@1570k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_hls-1800 mp4 704x396 1800k , avc1.64001F@1570k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_hls_https-1800 mp4 704x396 1800k , avc1.64001F@1570k, 50.0fps, mp4a.40.2@128k
iptv_streaming_1500_akamai_hls_open-2413 mp4 1280x720 2413k , avc1.640029, mp4a.40.2
iptv_streaming_1500_akamai_hls_open_https-2413 mp4 1280x720 2413k , avc1.640029, mp4a.40.2
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_hls-3117 mp4 960x540 3117k , avc1.64001F@2812k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_hls_https-3117 mp4 960x540 3117k , avc1.64001F@2812k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_bidi_uk_hls-3117 mp4 960x540 3117k , avc1.64001F@2812k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_bidi_uk_hls_https-3117 mp4 960x540 3117k , avc1.64001F@2812k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_hls-3117 mp4 960x540 3117k , avc1.64001F@2812k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_hls_https-3117 mp4 960x540 3117k , avc1.64001F@2812k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_hls-5510 mp4 1280x720 5510k , avc1.640020@5070k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_hls_https-5510 mp4 1280x720 5510k , avc1.640020@5070k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_bidi_uk_hls-5510 mp4 1280x720 5510k , avc1.640020@5070k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_bidi_uk_hls_https-5510 mp4 1280x720 5510k , avc1.640020@5070k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_hls-5510 mp4 1280x720 5510k , avc1.640020@5070k, 50.0fps, mp4a.40.2@128k
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_hls_https-5510 mp4 1280x720 5510k , avc1.640020@5070k, 50.0fps, mp4a.40.2@128k (best)