External SSD is not a substitute for soldered RAM.

No.

Virtual memory on an external drive will be painfully slow, even with a fast Thunderbolt SSD. RAM operates at nanoseconds, while even the best external SSD is milliseconds over USB or Thunderbolt. That gap is enormous.

The OS will try to swap data back and forth, and every time it hits the external drive, you’ll feel a stutter. It might keep the system from outright crashing, but it won’t feel usable. Think 1990s hard drive slow, but worse because your CPU is waiting.

If you need more memory, buy a laptop with upgradeable RAM or one with enough soldered from the start. An external SSD is great for storage, not for pretending to be RAM.