The Nothing Phone 3a Pro has space for two Nano SIMs in the same SIM slot (SIM 1 on the front and SIM 2 on the back), whether silver or black. I have the black one myself.
It also has two IMEIs.
Unfortunately, the manufacturer's spec page only says dual SIM and eSIM-capable:
The manual also says nothing about the SIM slot, only how to open it :-)
https://de.nothing.tech/pages...
The Swiss page is unfortunately only in English
https://ch.nothing.tech/pages...

We have ordered a black one. This one doesn't have dual sim. I can't say what it's like with the silver one.