Are there any truly FOSS networking options?

PFSense falls into this category for routers. Netgate makes hardware specifically for it, but you don’t have to buy anything from them to use PFSense. I only mention them because their hardware is good and you can buy anything from a normal home router to enterprise level gear.

I had to sign in with my ubiquiti account first before I could make a local account

I used to be pretty into ubiquiti, but this requirement really put me off. I have no desire to do anything ‘cloud’ with my router. This being a requirement sent me elsewhere.

TruNAS … What alternatives are there?

TruNAS has a community edition, so you could start there. Other alternatives are a standard Debian install, and use mdadm to setup RAID, then setup a network share in the OS, etc.