AS5404T

The problem you are seeing is unlikely to be due to RAM. Check the Memory tab of "Activity Monitor" to confirm; as long as the "Used" RAM is well under 4GB (it's normal for "Cached" to use up nearly all available RAM), you've got plenty of RAM. If you do choose to upgrade the RAM, the spec sheet say

Honestly, it's a pre-built NAS (ASUSTOR AS5404T) I did look a building a custom NAS, but it's hard to get close to 4 SATA Drives & 4 M.2 drives in a tidy enclosure for anything close to the same price point. (Even looking at a jonsbo N2 with the same CPU ended up costing more).

I had planned to buy the Asustor NimbuStor 4 Gen2 AS5404T NAS which has upgradable RAM & 4 SSDs, but it would've been €300 more in total.. (€150 difference from DriveStor 4 bay to NimbuStor 4 bay) I won't be using apps that need SSD speed like media streaming, VMs & stuff so I don't think it'll be