For anyone asking this question I might suggest Protectli. They've got x86 systems with coreboot. That's about as good as you can get these days for open source-ness without going really obscure or outdated. I've got a VP2440 as my router and firewall. You can neuter the intel management engine with coreboot, but there's still going to be firmware blobs somewhere in it, especially if you're trying to build a wifi ap.
One of my 2 pcengines APUs has developed an issue with its solder joints I suspect. It hangs at the bootloader unless the unit is already warm. Can't complain at all, it lasted ages and problems like this are just life for things that thermally cycle, it was in a pretty extreme climate for most of its life. Doesn't help with me needing a replacement now pcengines is out of business though, hence getting a protectli box.
This is the route I went. After a decade plus of shite consumer routers and finally an EdgeRouter which died (along with Ubiquiti's quality) I bought a Protectli box, build and flashed Coreboot and run OPNSense.
It's been going strong with regular updates (and by regular I mean as regular as your Linux workstation) for over half a decade now.
It wasn't cheap, somewhere in the region of £700 after adding SSD and RAM but it's a way, way overkill model and never exceeds 10% RAM usage and 15% CPU with an IDS running and a bunch of VLANs and Gigabit symmetric WAN.
My original goal for overspeccing it was longevity, but I regret it now, I want to upgrade to 10G+ networking and I can't justify replacing it when it runs so well and wasn't cheap.
One of my 2 pcengines APUs has developed an issue with its solder joints I suspect. It hangs at the bootloader unless the unit is already warm. Can't complain at all, it lasted ages and problems like this are just life for things that thermally cycle, it was in a pretty extreme climate for most of its life. Doesn't help with me needing a replacement now pcengines is out of business though, hence getting a protectli box.