I’m not 100% sure of the current best practice with Pipewire, but…
scsynth is oriented toward JACK. Pre-Pipewire, the JACK server uses ALSA (or other backend) to connect to the hardware, and this is the audio device selection. SC has no power to override that. This is why outDevices failed – it’s irrelevant in Linux.
If I recall, the way to use SC with PipeWire is 1/ “Install pipewire-jack for JACK support.” PipeWire - ArchWiki 2/ Start SC using the pw-jack wrapper e.g. if you’re using sclang in command line mode, pw-jack sclang; if the IDE (but I guess Raspberry, probably not this), pw-jack scide and child processes such as scsynth will be subject to the same (which you want). Server won't start: Pipewire on Ubuntu 22.10 - #5 by bad-numbers
Then the audio device selection would be done with pipewire tools.
I think… I’m not on a pipewire system.
Or you could drop pipewire and set up JACK in the old school way.
ALSA and PulseAudio settings will not help you at all – don’t waste time on those.
hjh