"How Does Using a Proxy Affect HTTPS Connections? Understanding HTTPS and Proxy Interactions"

HTTPS and proxy setups can be a bit of a headache, but you’re on the right track. The proxy can’t decrypt the data, but it can see the domain. If you’re worried about speed, try using a tool like WebPageTest to see how the proxy affects your connection.

And yeah, some proxies can act as MITM, but that’s usually not the case unless you’re using a sketchy one.