Self-Hosted Main

I use a subdomain for all my local services.

example.com then local.example.com and for the services service.local.example.com

This way i can still use Lets Encrypt but i also have a clear separation between actual services that are public facing and things i keep local only.

Fitting this to your setup when *.local.example.com points as CNAME to your local reverse proxy, then you can access it fine when at home. When youre away and your laptop tries to access it again, it still retrieves a local IP from the DNS, which of course fails, and because of that your webhoster at example.com doesnt receive any attempts at subdomains etc, you completely bypass it.

what happens to lan traffic when you leave the local network - home

it become wan traffic.

Should I be worried about sensitive data being leaked?

If you're not exposing any services over the internet...no?

Can you elaborate on this a bit more because I'm trying to figure out where you would arrive at that conclusion that it would be possible. Perhaps there's something in your setup that you haven't explained fully.

The processes that run on your laptop trying to connect your LAN services, would, outside of Lan, resolve the public DNS record and try to connect to the web hosting server. If the port is 80/443, they would indeed establish connection with the public web server, which could log those requests. This is when certificates and encryption comes into play. If your client programs are using TLS and are not buggy, and you have not uploaded your private certificate key to the public web server, they would just error out, and noting will be leaked. Split horizon DNS (what you are doing) is similar to DNS spoofing attack, TLS/SSL/HTTPS defeats such attacks. You secured your server (by not opening ports), but clients need to be secured too.

I set public DNS of my internal service hostnames to 0.0.0.0. That way if my internal DNS fails, it cannot resolve to a random IP