I encountered an issue with Cache Everything and Edge Cache TTL when using a WebP cache that occurs in Safari Browser.
Just want to alert others as the solution is very simple.
Safari does not currently support WebP images. There was expectation that Safari v. 14 would support WebP but this did not happen.
If you only check your Chrome Browser you may thing that eveything is fine.
But meanwhile, if you have WebP cache enabled and cached html, Safari Users may have pages that may fail to load images. With dynamic html this is not an issue, Safari will be served jpeg images. But with cached html Safari may be served with unsupported WebP files that do not display and can block rendering the page.
Disable WebP cache in your caching plugin and everything will be fine.
Check in GTmetrix that all images are served as jpeg once WebP cache is disabled.
It is not enough to just uncheck WebP in Polish in your Cloudflare settings.
Make sure to turn it off in your caching plugin as well and then reset the plugin cache.
Just by the way, there was no change to GTmetrix scores or speed.