This is also true for other older web browsers like IE 11, etc.
I have a free Cloudflare plan and “Speed > Optimization > Polish” is not an available option and my images are seen as broken in older browsers. My only option is to create multiple Page Rules in CloudFlare to get past this. I would have to use all 3 of my available page rules to tell it to not cache jpg, png, or gif. I can’t afford to use all of my page rules on this workaround.
This should be in your official documentation for the plugin, fallback support is not natively compatible with Cloudflare. It shouldn’t take me a half-hour of research to find this out.
My solution is to disable the webp option in your plugin. I can’t afford to lose 5% of my visitors for image optimization for the other 95%.