Uncapped FPS means more heat as you're letting your GPU render as many frames as it can possibly manage. It's not uncommon for this to peg GPU's at 100% usage at all times in games even in the menu screen.
For example my 2070 super instantly jumps to 100% usage in Vermintide 2's menu screen and heats up to ~72c. Then when I hop in the game the FPS cap setting kicks in and my GPU usage + temperatures instantly start reducing.
Lowering the settings will simply allow the video card to spit out even higher FPS, thus making lowering settings pointless with uncapped FPS if your goal is to reduce heat.
TL;DR: Capped FPS is the way to go if you want lower temperatures.