Waste heat will boil the oceans in about 400 years

Perhaps radiating fins built of an as-yet unknown material that could extend into space.

To read an entertaining work of fiction that deals with these issues I suggest Larry Niven’s Known Space series, specifically as regards the Puppeteer planet, and his World Out of Time book with extreme engineering solutions to climate changes.

Sabine Hossenfelder: All power plants create waste heat that contributes to global warming. At the moment, the contribution is fairly small, but if mankind flourishes it is bound to increase and eventually it will become a problem. The only thing we an do about it is to build an air condition for the planet.

Isn't there any material that generates electricity using such vastly available ambient heat?

There must be a thermal gradient, i.e. it doesn't work if everything is at the same temperature.

One end inside the ground and one in the air... Will that work? Maybe ocean instead of ground?