HTTPS (relying on
TLS) use encryption, but are based on an established TCP/IP existing connection. This means that even if the content is opaque, all TCP/IP information are in clear and available to someone sniffing your network.
TCP/IP information includes IP address of each peer, port numbers used. This gives a good hint about protocol and kind of traffic.
Some information may also be exchanged during the handshake, giving out some information. For example, if SNI is used (when multiple HTTPS web servers share the same IP), the name of the website is part of the TLS handshake and could be available.
As a side note, even being blind about the content can giveaway information. I know about attacks on interactive SSH sessions that measure the time between keys typed to deduce the commands executed, the typing habits of the person, and even what keys were pressed.