portable ssd for macbookpro

Just about any brand of portable SSD will work with the Mac if you make sure to format it for Mac use.

However, it's a good idea to stick with the name brands such as Western Digital, Seagate, PNY, Sony.

If the drive you buy comes with any drive utility apps intended to be used with the Mac, forgo those. They often cause problems and the Mac does not need them.

If buying an external drive to use for a Time Machine back up, be sure to buy one that has a total capacity that is 2x-3x the capacity of all the drives you wish to back up to it.

Types of disks you can use with Time Machine on Mac - Apple Support

SSDs available from OWC/macsales are a good bet. And the folks there also provide external enclosures that are compatible with the Mac.

The Thunderbolt 4 port is a.k.a. USB 4 and USB-C.

Any number of portable SSDs will connect to the USB-C port. If the drive has a USB-A type connector, then you simply need a USB-C to USB-A cable or adapter similar to this: