Still problems on Apple M1 pro. It took PM 15-20 minutes to load 80 images of 50Mb each. It mostly only shows one image or a bunch of empty placeholders. Then PM hangs for some minutes without showing any progress (not even the card read lamp shows action). Activity monitor shows that PM hangs. Somehow suddenly PM finishes and the yellow bar jumps from the beginning to the end and goes green (see screepdump for hanging matter). It's not usable in this state as on my previous MacBook it worked fluently.
I'll echo Kirk's suggestion to open up a ticket with us, but just wanted to add: I am fairly confident that this issue is not related to Photo Mechanic running under Rosetta.
I just did a test Ingest with a USB 3.0 card reader to an Apple USB to USB-C adapter plugged into my M1 Macbook Air, using a 30 MB/s CF card, with roughly the same amount of data as you described (3.5 GB) and it took about 3 minutes. Please get in touch by email or phone so we can look into why this is happening on your computer.