Selfhosted

Ah, so you added another nginx on the host by installing it from the package store of the distro and have that proxy port 80 to the docker nginx?

If you do that then you also need to add the websocket settings I had in the first comment to the host nginx.

What I meant what that the nginx in the docker-compose from lemmy also listens to port 80 and you just need to add

server {
    listen 80;
    server_name my_domain.tld;

    location / {
        proxy_pass http://localhost:LEMMY_PORT;
        proxy_set_header Host $host;
        include proxy_params;
    }
}

to the nginx.conf of the container.

Then you should have it accessable from port 80 without the host nginx (of course you need to stop the host nginx then).