To be fair the Synology lineup is confusing, but if you get the right model - one with a Ryzen processor and support for 32GB memory (officially; they can take more) - then you’ve got yourself a proper little workhorse with low power consumption, a stable, reliable OS, and super easy expansion thanks to the hot-swap drive bays and their Hybrid RAID option. My 8 bay model is running a couple of full-blown VMs and what must be two dozen or so docker containers while barely breaking a sweat. The DS723+ is the equivalent 2 bay model.
For things that need some acceleration like Plex and Immich I’ve added a little N100 box (a Beelink S12 Pro) with Ubuntu Server and another Docker instance, and mounted the NAS storage via SMB. This also sips power even when transcoding 4x Plex streams at once.
All of which is to say you don’t need to do a complex, potentially power hungry and difficult to expand self build to do what you want.