My theory is that the RTSP port (554) is for streaming and that when I go to the local address (that is on 80), the site ITSELF initiates a connection to port 554 in the background. However, this apparently does not happen when I connect remotely.
I think you’re on the right track here. The DVR is probably telling your browser to connect to 192.168.1.222:554 for the stream, which on LAN is fine because you have a route to 192.168.1.222, but when connecting externally you won’t be able to get to 192.168.1.222.
You can probably check the network connections in dev tools in the browser to confirm that.
Edit: Editing this to also stress the importance of the advice given by @SteveTech. My home cameras are also only accessible from outside my network via wireguard.