I generate a LetsEncrypt wildcard certificate for my domain name. On my home LAN, each device has a subdomain (
device.example.com). When those devices have a web interface for administration, I enable HTTPS and give the device the Let's Encrypt certificate to use. This allows you to administer the device without seeing scary warnings about security from your browser.
I installed FreshTomato on my router. Getting the certificate onto it is pretty easy if you use the script I wrote.