You are going about it the wrong way.
To connect those 2 Mac Mini together in Target Disk Mode, you would need a couple of expensive adapters. One adapter to go from USB-C to Thunderbolt then a second adapter to go from Thunderbolt to FireWire.
Do have a Time Machine Backup of the 2011 Mac Mini?
If you do, then the fastest and easiest way to move to the new Mac Mini, is connect the Time Machine backup to the new Mac Mini and migrate from it.
If you do not have a Time Machine backup.
Get an external drive, make a TM backup of the 2011 Mac Mini and use it to migrate to the new Mac Mini.
Or optionally Migrate Mac Mini to Mac Mini using an Ethernet cable connection between the two Mac Mini's.
Do not Migrate over your local Wi-Fi network as it will fail 99% of the time and cause you to have to do a start over.
see > https://support.apple.com/en-us/HT204350