This seems like it might be a perfect use case for Tailscale. The open source version of the control plane is called Headscale but you'd have to host it in a vps somewhere if you wanted to use it.

Tailscale is probably your best option.

Cloudflare Tunnels are black magic and exactly what you're looking for:

https://developers.cloudflare.com/cloudflare-one/connections/connect-networks/

Free, no need to self host a server somewhere externally. Can even be used for SSH!

frp, or just anything on awesome-tunnel at GitHub list

Do you have any external server available to you? If yes you could use that to set up a VPN connection or SSH tunnel.

OpenVPN

I use headscale and headscaleui but I've heard things about net bird and netmaker

I use zerotier. It's excellent.

If you are fine with ipv6, I'd use yggdrasil.

Just install it on any number of devices and each of them become part of a single «local» ipv6 network.

zrok

I use tail scale to get on the LAN and Rustdesk for desktops, webuis or SSH once in.

Yggdrasil Network might be an alternative.

It's a breeze to set up, just be mindful about setting up your firewall and allowed keys, depending on your use case.

If you already own a domain name, you could use Cloudflare tunnels using cloudflared (it's free).