You haven’t really given enough information about your config to diagnose.

If you’re able to access it from your local network but not your outside network it’s a port forwarding/firewall or routing issue. My guess is it’s a firewall issue either on your network edge (likely integrated into your router) or on your server that’s hosting immich.

Unless you do one of the following you won’t be able to access it from outside your network:

-set up a VPN and tunnel into your network. Wireguard or tailscale/zerotier will be easiest.

-set up port forwarding correctly. Not my first choice, best to VPN in rather than poke holes in your firewall, especially if you’re a noob.

-set up a reverse proxy. This is a bit more complicated than a VPN or overlay VPN (tail scale etc), but it works fine and will be secure as well.

If you haven’t done one of those three things then you won’t be able to access anything from outside your network, for good reason - your firewall is by default set up to deny connections that are initiated from outside your network, so when you’re trying to connect from the outside it looks at your traffic trying to start a connection to your server and naw dawg’s it.