Not sure if anyone else mentioned this, but you can just redirect traffic on your local LAN with an ad blocker like pihole ( I currently use adguardhome podman instance )

Basically, it rewrites any calls to your outside domain from within your local network, back to your local web server. As long as the site is setup with the certificate there, you’re good.

Then setup a nginx reverse proxy and you’re golden. Regular site outside LAN, internal site inside LAN.

Edit: spelling