So, the 4.6V is consistent with the schematic for the Stamp-S3, I see.
The EN is connected to VIN, not VCC, via a diode, which drops it a little below the 5V from USB.
This is different from the Stamp-C3, but I guess that's fine.
@bram The EN is the Reset input and is pulled up normally, and brought down to reset the ESP.
While it does seem odd that it is 5V, mine does the same thing!
My (ahem) LilyGO T-Display S3 Reset pin is at 3.3, which makes more sense.
-Terry