External RAM via Thunderbolt is not a thing.

No.

RAM needs to be directly on the memory bus, connected to the CPU with incredibly low latency. Thunderbolt, even with an eGPU enclosure, is a high-speed peripheral connection — not a system bus. The enclosure is designed for PCIe devices (like graphics cards), not for plugging in DDR5 sticks and having the OS treat them as main memory.

Some clever folks have experimented with NVMe-based swap or RAM disks over Thunderbolt, but that’s storage, not system RAM. It’ll be slower, less efficient, and the OS won’t recognize it as additional soldered memory. Modern operating systems don’t have a mechanism to “add RAM” over an external cable.

If you’re stuck with soldered RAM, your only real workaround is to use swap (virtual memory) on a fast external SSD. It’s not the same as having more RAM, but it’s the closest you’ll get without buying a new machine.

This is where you make the right purchase the first time.