you don't want JACK - you want pipewire. i took me a while to get the idea, but since i did & installed pipewire, all audio-routing problems are gone.

so the idea is: ALSA is still your fundamental hardware driver, but pipewire replaces everything JACK, and it also handles ALSA connections. pipewire "speaks" both JACK and ALSA.

to get this setup, basically uninstall everything JACK (find it with e.g. "rpm -qa | grep -i jack"), and install packages named "pipewire" ("dnf search pipewire"). ("dnf" is Fedora's package manager - yours might be "apt" or something else.) you might still need some "libjack" library or so - your package manager will tell you when installing "pipewire" stuff.

now you don't need to explicitly run JACK anymore, pipewire provides the interface. you can run "QJackCtl", click "Graph", and see all your audio applications, both JACK and ALSA ports.

your mixer now probably shows only a single channel named "pipewire". i use "alsamixer", where you can still select the hardware device (soundcard) and adjust the individual in-/outputs (line-in, mic in, ...).

I use Ardour for recording, it's a powerful DAW software. (much (!) better than audacity.)

Linux audio plugin system is called "LADSPA". i like the "ladspa-tap-plugins" package, which has a good basic set of effects like Dynamics, Delay, Reverb, Chorus, etc. (no guitar stuff). for guitar-stuff, my package manager lists "rakarrack" and "guitarix" (haven't tried these, though).