Oh yes. You're taking about a VPN.

But that opens a whole can of worms. You could go with something more tried and true, like Ike/IPsec, if your routers have that option. Usually that's the way for firewalls, but it's a bit hit and miss for routers.

Or you can go with something a bit more modern, like tailscale, wireguard, or zero tier. But then you need some way to put that on your NAS. I'm partial to zero tier, but there's plenty of good options, even beyond what I've mentioned.

Researching this becomes a mine field without the right vocabulary, because having a "VPN" is such a broad definition that there's a lot of commercial VPN solutions, designed to give you operational security when browsing the Internet, which are completely useless at securing traffic between computers on different LANs over the Internet. Services like PIA, NordVPN, surfshark, proton VPN, Express VPN.... So many others. They'll secure your traffic to the Internet itself, not between private locations connected by the Internet.

I don't know what hardware you're specifically using as a router at each location or what works with what. I know ubiquiti has some VPN features in their gateway products, and that could make quick work of the problem. Just food for thought I guess.