What am I missing? This looks like a re-encode:

    $ yt-dlp -x --sponskrub --sponskrub-cut "https://www.youtube.com/watch?v=_7vPNcnYWQ4"
    [youtube] _7vPNcnYWQ4: Downloading webpage
    [youtube] _7vPNcnYWQ4: Downloading android player API JSON
    [info] _7vPNcnYWQ4: Downloading 1 format(s): 251
    [download] Destination: Making an unpickable lock. Calling locksmiths [_7vPNcnYWQ4].webm
    [download] 100% of 12.72MiB in 00:00
    [ExtractAudio] Destination: Making an unpickable lock. Calling locksmiths [_7vPNcnYWQ4].opus
    Deleting original file Making an unpickable lock. Calling locksmiths [_7vPNcnYWQ4].webm (pass -k to keep)
    [SponSkrub] Trying to remove sponsor sections
    WARNING: Cutting out sponsor segments will cause the subtitles to go out of sync.
    [libopus @ 0x5462c20] No bit rate set. Defaulting to 96000 bps.
    size=    3515kB time=00:04:33.53 bitrate= 105.3kbits/s speed=  26x

Without the audio only option, it's more clear it's re-encoding:

    [SponSkrub] Trying to remove sponsor sections
    WARNING: Cutting out sponsor segments will cause the subtitles to go out of sync.
    [libopus @ 0x5575420] No bit rate set. Defaulting to 96000 bps.
    frame=   51 fps=8.5 q=0.0 size=       1kB time=00:00:01.95 bitrate=   3.5kbits/s speed=0.326x