I saw the term "Thermal Pollution" come up, and that sounds like it could be what I'm thinking of.
I often see folks hanging out in their vehicle idling with the AC Running, and think about how inefficient it is. Of course, A/C systems simply "move" the heat from inside the vehicle to outside of it- But an idling engine in the mix is just a huge waste.
The global surface area of Earth is 510,067,420 km2. Dividing through, this works out to 7,525 W per km2, or 0.0075 W/m2. This assumes that all energy used by vehicles ends up as heat, which is a rough assumption, as only 12 to 30% of the energy used by a car is converted to kinetic energy.
In contrast, the sun radiates an average of 340 W/m2 to the Earth's surface.
This is why, despite being only 20% efficient, solar PV could power the world if each country had 100 km2 array, or about 500,000 km2 globally. That's a lot, but still less than 1/10 of a percent of the earth's total surface area.
As comments have pointed out, directly comparing waste heat from vehicles to solar irradiance isn't valid, as these energy sources are coming from and going to different places. But understanding how much greater the sun's energy is (by a factor of nearly 50,000) helps explain why there's more concern about the heat-trapping CO2 from vehicle exhaust, then the heat they directly put into the atmosphere.
Osaka Heat Island Countermeasure Technology Consortium (HITEC) was established in January 2006, for the purpose of the development and spread of heat island countermeasure technologies, implementation of measures and verification of their effects, and the collaboration between industry, academia, government, and the private sectors [15].
https://www.sciencedirect.com/topics/engineering/anthropogenic-heat
This next article doesn't say how much this effect causes heating compared to greenhouse gasses alone, but it confirms that it's a fairly local problem in section 2. It also says that to help reduce this effect, we need to reduce the creation of greenhouse gasses. From how I read it, this means that anthropogenic waste heat and greenhouse gasses aren't two different problems, but intertwined. Not to mention that most of this anthropogenic waste heat is created by industries and homes releasing greenhouse gasses to create the heat they use and release.
Cool roofs reduce building heat-gain, create saving air conditioning expenditures, enhance the life expectancy of both the roof membrane and the building’s cooling equipment, improve thermal efficiency of the roof insulation, reduce the demand for electric power, reduce resulting air pollution and greenhouse gas emissions, provide energy savings, and mitigate UHI effects.