Flip a switch and then what, are you getting a isolated public URL to share? Or you have your infrastructure exposed to the internet and the shared URL is pointing to your actual server where the data is hosted?
I think the previous commenter misunderstood your question, this is the answer (you can also put it behind something like cloudflared tunnels).
Immich is a service like any other running on your server, if you want it exposed to the internet you need to do it yourself (get a domain, expose the service to the internet via your home ip or a tunnel like cloudflared, and link that to your domain).
After that, Immich allows you to share public folders (anyone with the link can see the album, no auth), or private folders (people have to auth with your immich server, you either create an account for them since you're the admin, or set up oauth with automatic account creation).