Ideally one that can use more than one disk so that i can expand it later when i can. Have some minimal experience with Synology since there’s one at work and i have interacted with it a couple times and like the interface, but am not married to any brand as long as it works.
Located in EU if it makes any difference.
Really any PC could be made into a NAS. If you have any old PC laying around you can install Linux to it, and then set up disk shares. I’m assuming you mean an appliance like NAS and honestly the only one I know of, but never used, is Synology.
The Lenovo ThinkCentre computers are great for this. I got one off eBay for $30 (just make sure it comes with their proprietary AC adapter).