A lot of the SBCs or n150 pcs have limited RAM upgradeability.

You might look at the old HPE Proliant Microservers, like gen8 - gen 10. You can get them with 16GB ram included for $300. They’re low power and they use the cheaper ddr4 ram.

SYS-A22GA-NBRT

The $500,000 10U AI server or is there another one?

I still can’t add 3rd party software that isn’t in their App Store

That doesn’t seem right… I think you can use their “Container Station” to make an LXD or Docker container with whatever you want. You may have to enable “advanced mode.” https://www.qnap.com/en-us/how-to/tutorial/article/how-to-use-container-station-3