If you have the money to buy a synology of some sort squared away, here’s how to make something better(?) for a fraction of the price:

Buy a used drive shelf. It’s the part in a server rack with all the drives in it. It plugs into a sas card to move data around and into a network switch to be managed. Get one with all the drive sleds present - $2-3 hundred for one that can take about 24 3.5” drives.

Buy some cheap sff pc. These things are everywhere and they have all you need for a little server. Favor cores over threads, 16gb of ram is more than enough but you can easily add more later. anything in the seventh or eighth generation of intel chips or later is fine. ~$30

If your sff pc has a second Ethernet port, that’s cool! It’s okay if it doesn’t, but if you want the option of a management subnet then you can add one in a half height pcie for almost no money.

Another option is a video card to handle decoding media. When you stream some crap to your tv or set top box or whatever, it needs to be decoded. Most of the time those CPUs are tough enough to do the job but for 4 or 8k media using recent encoding schemes, a half height video card is useful. What’s nice here is media decoding is insanely solved as a problem, so a $50 card will be overkill as long as it natively supports your target formats.

Buy a hba card and the wires to connect it to your drive shelf. You want a half height hba with external connectors that are the same or later in spec than your drive shelf. You can get sas wires that are terminated for 80xx on one end and 86xx on the other end. $50-100 for the card, $20 for the wires.

Plug it all up, put in your drives, install whatever dumb software you wanna use and you’re off to the races with the capacity to use 24 disks for 300-450.

The downside:

You have to have somewhere to put it. You’d need somewhere to put your synology too, but a relatively quietly humming shelf of drives that would look more at home in an industrial environment belongs in the closet, not on the same credenza some people like to put their synology.

You’re actually responsible for it. There are fewer guardrails and if you don’t make backups you can just lose data or end up with a broken system. You’re already using a system you’re responsible for though, so this would just be a bigger better version of what you have that doesn’t go into conniptions like rpi type beats does.