How long did you wait to visit the site after adding it to pangolin? I ask, because if you set it up and go within 30 seconds of saving you may see the cert warning initially. It can LetsEncrypt time to verify a site and issue a cert. it’s usually pretty fast, but I’ve seen it take up to 30 seconds or a little longer.

I’ve hit the same thing where I setup a site through Pangolin and go to it too fast, but if I just close the tab and wait about 20 seconds then go again, it all comes up with a proper cert. hope that helps.

Cheap VPS with Pangolin for Wireguard and reverse proving through the tunnel.

This!

If you can get It’s blessing I’d suggest something like KASM workspaces or WebTops, basically a Linux desktop in the browser.

This!