We appear to be confusing each other.
My last 2 posts were on the basis that you had borrowed an old mac with a FireWire port and you were asking what cable was needed between Mac and camcorder.The cable needed for this set up is the 9 pin to 4 pin FireWire cable pictured earlier above.
No other cables or adapters are required and no "drivers" either.
First questions; Did you try to import into the old borrowed Mac using the FireWire cable? If you did what was the result.?
Did you try capturing using Quicktime Player and iMovie.?
What OS is it running and what version of iMovie? Or have you abandoned the idea of using the old Mac?
Now back to your new Mac.
"It’s a USB-C to USB adapter and I’m on Big Sur. I do have the other 2 adapters as well but to no avail. "
Can you send picture of USB-c to USB adapter . The only 2 adapters you need for your new Mac are these 2 numbered 1 and 2 in this picture.
Neither of them is a USB-c to USB adapter.

These 2 adapters are used together with the 9 pin to 4 pin FireWire cable pictured in previous post.
It has been stated that capturing tape with newer Macs and newer OS appears to have become more unreliable .
It certainly works for some but not all . The old Mac should be OK.
When you reply can you be certain to indicate which answers refer to the old Mac and which refer to your new Mac?