Flexible would break it, the reason why he has that issue is because CF was on Flexible, sending http requests to Google, and Google was responding with a redirect to https
You should really use Full (Strict) in all cases, all other settings are lying to the user about security/not fully secure, or Off if you don't plan on having https
Full (Strict) is the same security/validation (mostly) as the browser has for ssl certs. Full is "accept any, even self-signed", and Flexible is http to origin, even if visitor is over https (very insecure & lying to visitor)
one day hopefully Cloudflare will just nuke the other settings, one can hope. I've heard recently that the default should be "Full" now, but not sure that's the case
Even if it was https to origin, you'd still be http to CF which would be insecure, if you wanted security, use Always Use HTTPS and avoid that path entirely