Honestly, you can roll your own, and that's great for a tinkerer and someone who manages their own infrastructure like a home lab or the like. It works, it can be cheaper, and you get what you spec. Maybe it's too easy actually, since you can screw it up and if you have the right backups then it's time wasted setting it straight, and if you didn't have the backups, then WTF get your head on straight.
You can buy something pre-rolled. Synology has great software, and while I think the hardware is a bit underwhelming, it gets the job done unless you're trying to run your whole setup on the NAS which even tho the software can do, it's gonna fall on it's ass with a bunch of containers etc running. QNAP, while I don't have the experience, can do it too. Synology or similar would be my first stop for someone who's looking for something to get going with and wants it stable and maybe it can do a little more besides.
Beyond that tho, like most things, you will shift the bottlenecks around in your setup - if previously you needed more space, well now you got a ton, only it's not quite as fast as you were hoping. Honestly once you got backups sorted and a good reliable platform, the next frontier is networking - 1GbE is just not fast enough, IMO, for modern arrays. 2.5GbE should be the minimum and 10GbE is really where you should aim, and really it's not that much more expensive anymore. But of course this means you might need new cables, a new NIC, a good router or switch, maybe an add-on card for the NAS, etc. But you should consider network before you consider other options, like caching or memory upgrades, etc. Seriously, it makes a huge difference. Unless you're on wifi - then you're stuck until wifi 7 is common.
Good luck!