Yes, the device is compatible with your iMac from 2020. It works via USB-C with USB 3.2 Gen 2 (up to 1000 MB/s), as Macs do not support USB 3.2 Gen 2x2, but the port is downward compatible.
Do you have a usb3 connection on your pc or do you still have the old usb connections on your pc - that will be the reason - a fast hard drive is only faster on a PC that is already up to date with the appropriate mainboard etc.