So as I said, the script has no problem with the URLs. It runs in bash even if you run it from zsh.
EDIT:
Just tested the version above (with a random video) and it works. I use zsh btw.
Output
% ytdlp-simple
[youtube] Extracting URL: https://www.youtube.com/watch?v=B9FzVhw8_bY
[youtube] B9FzVhw8_bY: Downloading webpage
[youtube] B9FzVhw8_bY: Downloading ios player API JSON
[youtube] B9FzVhw8_bY: Downloading android player API JSON
WARNING: [youtube] Skipping player responses from android clients (got player responses for video "aQvGIIdgFDM" instead of "B9FzVhw8_bY")
[youtube] B9FzVhw8_bY: Downloading player 74a3a562
[youtube] B9FzVhw8_bY: Downloading m3u8 information
[info] B9FzVhw8_bY: Downloading 1 format(s): 313+251
[download] Destination: The Dead South - In Hell I'll Be In Good Company [Official Music Video] [B9FzVhw8_bY].f313.webm
[download] 100% of 500.13MiB in 00:02:42 at 3.07MiB/s
[download] Destination: The Dead South - In Hell I'll Be In Good Company [Official Music Video] [B9FzVhw8_bY].f251.webm
[download] 100% of 3.33MiB in 00:00:00 at 3.64MiB/s
[Merger] Merging formats into "The Dead South - In Hell I'll Be In Good Company [Official Music Video] [B9FzVhw8_bY].webm"
Deleting original file The Dead South - In Hell I'll Be In Good Company [Official Music Video] [B9FzVhw8_bY].f251.webm (pass -k to keep)
Deleting original file The Dead South - In Hell I'll Be In Good Company [Official Music Video] [B9FzVhw8_bY].f313.webm (pass -k to keep)