I have used these: https://www.crucial.com/products/ssd/portable-ssds
They work great.
I also have a few m.2 nvme/sata enclosures.
I like this one the most - https://www.amazon.com/gp/product/B08RVC6F9Y
I basically just reuse old m.2 SSDs in them and they are functionally the same (and potentially more reliable) as the portable SSDs you can buy.

What features do you use Macrium for?

Honestly if you are only dealing with windows, and only looking for imaging, it might be better to just run a dism.exe script like this one: https://github.com/KyodaiKen/DISMBackup on a schedule.