You can tell PulseAudio to ignore certain audio interfaces:

<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 ...