nginx – How to forward HTTPS to HTTP for any IP address?

I have an iFrame in an HTTPS site. This iframe must point to an IP (not specific, there are hundreds of different ones) in HTTP. Currently, it doesn’t work: “This request has been blocked; the content must be served over HTTPS”
I imagine that one solution would be to use a reverse proxy but I can’t find how.

The basic config would be:

HTTPS web server with iframe to HTTP (> Reverse proxy with catch all HTTPS>HTTP ( -> Device (IP like 192.168.0.x)

How can the proxy receive requests to device IPs since it does not own each of these IPs?
How to redirect HTTPS to HTTP on the same IP?