What external portable ssd 2tb do you recommend with the Thunderbolt 4 interface?

Note that Thunderbolt 3 and Thunderbolt 4 are cross compatible. There are no speed differences between the two.

Also, what is the external drive going to be used for because you may not need the speed or the cost ($$$) of a Thunderbolt drive.

FWIW, I have an OWC Envoy Pro SX 1TB SSD and it has been working quite well for me.

The OWC Envoy Pro FX or SX.

https://eshop.macsales.com/shop/external-storage#drive-configuration:single-bay-1-drive

There is the new OWC Express 1M2 external enclosure. I would confer with OWC on which NVME M.2 2280 format SSD drives they have tested with it before you make the purchase — if you want to use a separate drive purchase. The Crucial drives are quite fast, but best to know compatibility beforehand.

I use the Acasis and Trebleet enclosures. Both work fine.

All depends how fast you want the drive to be. I use a WD 2TB NVME drive in a TB enclosure for max speed.