Just add this line on your nginx config file, on server block. It hangs because a request is send over http instead of https.
add_header 'Content-Security-Policy' 'upgrade-insecure-requests';
I tried with Odoo 16 CE, on ubuntu 22.04, and it works fine
Misleading! The error may not be related to the proxy.
Analyse the console log (F12): If the browser blocks the request, the proxy has no chance to react and this is a bug of the website editor.
Even the "latest" Odoo 16 Community build has this error.
Thanks Gregor for your comments. Is there a workaround to solve this issue meanwhile the bug in Odoo Website is fixed?