Samsung t7 "Shield" in 1tb size is what you want:
Samsung T7 Shield Portable SSD delivers high performance on-the-go, not matter the terrain. It has an IP65 rating for water** and dust* resistance, with Dynamic Thermal Guard to manage heat control. Transfer huge files instantly. USB 3.2 Gen 2 and PCIe® NVMe™ achieve soaring sequential read/write...
www.amazon.com
I have one myself, very nice.
It will serve you well.
Some additional tips:
When you get the new SSD, IMMEDIATELY ERASE IT to the format you will be using.
You DO NOT NEED any manufacturer software that comes on the drive.
If the drive is going to be used FOR DATA STORAGE ONLY (not bootable or not a tm backup), erase it to "Mac OS extended (journaling enabled), GUID partition format".
If you need it to be bootable, or will use for a tm or other backup, then it will need to be erased to APFS, GUID partition format.
One other thing about using an external drive for "primary external storage" for files that ARE NOT on your internal drive:
Now, you have a SECOND drive that needs to be "backed up" to prevent against data loss.
YOUR DATA IS NOT SAFE on only one drive.
This means you also need A SECOND EXTERNAL DRIVE to serve as a backup to the SSD.
You could use a cheap platter-based drive for this job.
I would recommend using either CarbonCopyCloner or SuperDuper to regularly "update" the backup -- doing so will create AN EXACT COPY of the original.