Yes, you can use KeepMyNumber with an eSIM.
KeepMyNumber is carrier-independent, which means it works on any device that supports the app — whether you’re using a physical SIM, an eSIM, or both.
If your original number is on a physical SIM, and you switch to an eSIM for local data abroad, you can still receive calls to your original number through the app — as long as call forwarding is correctly configured.
Conversely, if your original number is already on an eSIM, you can set up forwarding from that to the app just like you would with any regular SIM.
Just make sure your device supports eSIM (most newer iPhones, Pixels, and some Android flagships do).