I'd like to install a uSD card in EISY to store some audio files for playback via this plugin.  I'm familiar with Debian Linux tools, but the EISY OS lacks most of those.  I'm looking for the steps necessary to do this, how the card should be formatted, (ext4?), how it will appear in the device list, necessary permissions etc. I'm logged in as admin: should I continue as admin or add a user?  I've reviewed most of the posts here, but most are old and incomplete.  Thanks, as I think there may be others that want to do this as well.  An up to date tutorial on the subject would be great!

Not too sure if this will be what you need.

https://developer.isy.io/blog/NVMe/

Yes, that will help.  After reading a few more posts, I should have asked if the SD card slot on the EISY is actually supported.  That arose in another older post and was never answered. If not I'll just get an SSD and install it. if no response in 24 hours I'll open a ticket.

Michel says the SD card slot is not supported - so much for that idea.