The cables that you require are listed in the following link.
The adapter that you refer to would not have been supplied with the camera from new as USBc is a far more recent concept than Mini DV camcorders.
Your USBc 2017 Mac would require the 2 adapters mentioned but your older Mac might only require the one, depending on it's age. Better still if your older Mac has a FireWire 800 port then all you need is the FireWire 800 cable, sometimes referred to as 4 pin FireWire to 9 pin FireWire cable, as in the link.
In any case of course you need the FireWire 800 cable to connect to your camcorder.
In this link the OP refers to VCR tapes (they mean Mini DV tapes) and also FCPX but the cables are the same for iMovie.
https://discussions.apple.com/thread/251304950
And yes you may have more success with an older version of iMovie on an older Mac with older OS.