You can tell PulseAudio to ignore certain audio interfaces:
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https://lukas.zapletalovi.com/2020/07/force-pulseaudio-to-ignore-a-card.html>
Hooray! PulseAudio no longer touches my Focusrite Scarlett Solo now, so
I can simply dedicate it to JACK. I used to shut down PulseAudio
whenever I needed to run Ardour or Guitarix, which was pretty
annoying ...