How do I fix the comfort of my bike? On a folding ebike with no suspension what’s the best addition to help with uneven roads bumpy surfaces etc?
Whats the best/valued part I could add for comfort please?
The first things I look at to smooth out a ride are:

Least expensive: Tire pressure. Printed on the tire is the recommended maximum inflation. You can experiment with lower tire pressures to smooth out the ride. I'd try reducing tire pressure in 2 PSI increments and then testing at each step. The downside to reducing pressure is increased rolling resistance and at some point you risk bottoming out the tire against the rim on a bump causing a puncture in the tube. If you keep an eye on your tires as you test you can avoid this outcome.
Look for a softer seat. A seat with more padding or springs will soften the ride. Some people like padded seat covers.
Wider tires. How wide a tire you can use depends on your frame. Wider tires allow lower pressure and smoother ride