Images is not shown on iphones/macs using "Icloud Private Relay" when caching is enabled

Hi,

Scenario:

1. Do a clean NPM setup SSL, Caching enabled etc. - pretty standard stuff
2. Setup an apache server in the backend
3. Setup a standard wordpress
4. Use a Iphone or Mac with "Icloud Private Relay" enabled.

Result:

1. The site does not load at all, this can be fixed with by adding this in advanced configuration on the site in NPM:

proxy_hide_header Upgrade;

Now the site will load - but wont show any images - however turning of the cache will fix that issue - which is not really optimal since i want to use NPM to lower the load on the backend server.

My question is:

1. Why does this happen ?

2. How can it be resolved ?

Notes:

1. Using another browser without "Icloud private relay" works fine or even just turning it off - but this is not a optimal solution either since you never know what the scenario of the visitor will be.

Reproduce the reported Nginx Proxy Manager setup with caching enabled, an Apache backend, WordPress, and iCloud Private Relay. Compare behavior with proxy caching disabled and with the proxy_hide_header Upgrade; advanced configuration. Done means the site and its images load while caching remains enabled, without requiring that workaround.