No, attenuation in vacuum is exactly the same, and the difference between humid air, dry air, and vacuum doesn't really matter at frequencies below a few GHz.

> For example, attenuation at 1 km for 144 MHz (ham VHF band) is about -76 dB while for 2.4 GHz, it is about -100 dB.

This is a common misunderstanding of the free-space path loss formula, which is expressed in terms of the idealized isotropic radiator, the length of which is frequency-dependent. In other words, this calculation is assuming a proportionally (much) smaller antenna for the 2.4 GHz case.

With the same antenna size, the path loss is exactly the same. After all, where else should the radiated energy go?

> With the same antenna size, the path loss is exactly the same.

What do you mean? The size of the dipole or monopole antenna is dependent on the wavelength, so obviously the 2.4 GHz is just a few centimeters and not the same size as a VHF antenna.

> After all, where else should the radiated energy go?

Well, most of RF energy is wasted. There are software that can plot the radiation pattern, but even without knowing the exact pattern, very little RF energy is received at the target.