Use an external SSD as your startup disk with your iMac or Mac mini

You cannot use the Intel external drive to boot the new Mac as the hardware is different. I have tested that and it does not work even though the OS is the same..

I have one secondary thought to offer. Sometimes I have found that various other drives need to first be erased and reformatted using Disk Utility - not the maintenance utility that often comes with such disks. They often cause connection problems.

Check the bus speeds versus the drive speeds.

A really fast SSD will be limited by the I/O connection, as external connections are longer and thus usually slower that internal.

Performance is based on the slowest component.

A fast CPU always waiting for an HDD is wasted.

With that caveat aside, most external SSD stuff will work fine.

Potentially at bus speeds, not at SSD rated speeds.

If the storage lists macOS support, all the better.