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.

Invest in Apple.

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

This!