Will the environmental impact of Bitcoin improve once the last coin is mined?

I understand that once the last Bitcoin has been mined, there is a mechanism where transaction fees can be added and that would become the predominant way the nodes would make money over mining.

What I was wondering is what this means for the difficulty of the problems? Do they just keep getting increasingly difficult forever, or am I right in thinking that once all the bitcoins are “out” then, the difficulty could decrease as less people are mining, and so less energy would be spent.

Apologies if this is a stupid question - and not trying to straw man a debate around the “greenness” of Bitcoin.

I’m just genuinely curious about the future.