DPI is distinct from TLS MITM (though many enterprise devices offer both).

The delineation here is between "shallow" packet inspection (which basically nobody refers to because it's just a normal part of networking), where network devices look at just the bits of the packets they need to route / NAT / etc them appropriately.

DPI can tell a ton of things without needing to MITM encrypted layer 7 traffic.

A boring example is that you can tell TLS from OpenSSH traffic just by seeing the initial handshake. sslh ( https://github.com/yrutschle/sslh ) takes advantage of this on the server side to let you run both on the same port.

A less boring example is identifying OpenVPN, Wireguard, etc traffic regardless of what port they're run on, to enable blocking VPN traffic on a network.