If a professional had access to darkroom facilities pretty much everything could be done in there right down to removing people and background objects (see for instance https://rarehistoricalphotos.com/stalin-photo-manipulation-1...).

It's just far easier for anyone to do now.

I know. You can remove people, use selective exposure with dodge and burn, etc.

But you can't change a person's proportions and skin tones so precisely unless you're printing small and have time, equipment and talent to paint the positive (negative would be nigh impossible) in a believable manner to do so.

On the otter hand, you can enable slimming filter on your phone or camera, click and you go.

Oh, also, some of the Soviet photo manipulation is done with stolen and translated French software, in 1987 [0].

[0]: https://tech.slashdot.org/story/10/11/04/1821236/soviet-imag...