Best External drive combo for Mac Mini M4

That appears to be a USB4 40 Gb/s enclosure.

40 Gb/s = 40,000 Mb/s = 5,000 MB/s maximum data transfer rate before overhead. In practice, there is always some overhead.

As far as data transfer rates go, it's only editing video with really high resolutions where you would be concerned about the speed of a drive like this. I've read of people using Lightroom storing all of their full-size photos on old-fashioned mechanical hard drives (top speed: about 150 MB/s) and only putting their catalog and cache files on a much faster SSD. That works, because even if a full-size photo file takes up 20+ MB, you're not reading or writing the file that often (outside of the context of making a backups).

Over and above what Servant of Cats said, avoid daisy-chaining through slower hubs or docks—plug directly into the Mac mini’s port. You may use this app to test the read-write speed.

Blackmagic Disk Speed Test 4+

Simply click the start button and Disk Speed Test will write test your disk using large blocks of data, and then display the result. Disk Speed Test will continue to test writes and reads from your disk so you can evaluate both performance and readability over time.

Blackmagic Disk Speed Test on the Mac App Store - Apple

As far as I know, Macs do not support USB 3.2 Gen 2x2. I believe that USB4 defines three different and incompatible “up to 20 Gb/s” USB transfer modes. A USB4 host port must support USB4 20 Gbos mode but is not required to support USB 3.2 Gen 2x2. In effect, the USB Implementer’s Forum has allowed Apple and others to throw USB 3.2 Gen 2x2 under the bus.

Your M4 Mac mini supports USB4 20 Gbos, USB4 40 Gbps, and Thunderbolt 4. I haven’t heard of any USB4 20 Gbps enclosures; maybe vendors think that there would not be enough of a market for them.

Note that USB4 40 Gbps is not the same thing as Thunderbolt 3/4, even though all three run at up to 40 Gbps, and USB4 40 Gbps mode is based in part on Thunderbolt technology.