Is radiation from electronic gadgets harmful

No it isn't you silly.

People are confusing radiation from any radiant source with ionizing radiation.

Frequency

2.4 GHz is way below 400 THz, where IR transcends to visible spectrum. It is non-ionizing, unlike X-rays and Gamma Rays.

Even body heat is radiation in the IR range.

All heat is simply radiation.

Intensity

Routers emit radiation at 0.1W.
Microwave emits 2.4 GHz at 1000W.

This is 10000 times more than a router.

The Sun emits radiation of all frequencies, and about 100 THz - 1 PHz reaches the ground, at around 10W. This ends up being hotter than a microwave.

Body heat makes you much warmer than routers.