Since you want to go the Raspberry Pi route, I assume you're a novice Linux user on a budget.
Within you're chosen route, I recommend running a Raspberry Pi (preferably the 4 with 2+ GB of RAM) with OpenMediaVault.
However, a 3B would be perfectly fine for the job if you only want NAS (no torrent, streaming / DLNA server and other services).
There are plenty of manuals to setup a Pi with OpenMediaVault. Just Google for it.
You're looking for a manual for the Pi 4 with OpenMediaVault 5 at the moment of writing.
If those manuals read like gibberish for you, I can only say go for a Synology (but it will cost you $$).
Not to sound like a jerk, but if you can't Google for where to buy a RPi in your country, maybe RPi + OVM is not the way to go.
However, with adequate effort, users (or I) will happily help you setting up your RPi + OMV.
That means you have tried yourself, can exactly tell what you've done and what's going wrong.
Just a note: I hate using RPi. SD card wear and tear is a real thing.
Minimizing reads and write can significantly expand the lifespan of a SD card.
For me personally, it's still too unreliable.
If you want something reliable too, again, buy a NAS.
Or build your own (low-energy) server with OVM instead of using a RPi.
The self-build route can be cheaper than a Synology NAS, but more expensive compared to using a RPi.