Github guide from 2021 is using realtimeconfigquickscan script that has been archived and replaced by rtcqs script. but relatimeconfigquickscan-git and rtcqs are both available from AUR
Sophomoric blog from 2020 is using a smaller set of realtime configurations from Professional audio - ArchWiki
( sudo systemctl… 
)
Unfa’s KDE-specific video is also from 2020 but is using the ‘original’ howto
System configuration [Linux-Sound] – wiki.linuxaudio.org
(Unfa can delete youtube messages but cannot delete forum posts The state of Linux audio and JACK)
Does ALSA show digital output or input subdevices in aplay -l; arecord -l ?
For an external hardware mixer connected via USB (or firewire) I would suggest checking out linuxmusicians.com forum. You could also ask AVLinux developer (GMac) about Audacity issue on there
If you use ALSA more than JACK check out Ardour forum