Fixed Super Light Super Safe

usually around the 145psi which is fine if you're running 100-120

Thats for metal clincher rims, and even for metal rims it can be a fair bit lower than that. A decent chunk under what is pinted on your tyres

Carbon fibre isnt great under the sort of focused tension a rim bead undergos. So is likely worse.

The issue with carbon fibre rims is one of heat- whilst alluminium (being a metal) conducts heat very well, carbon fibre is essentially an insulator, and holds onto heat rather than conducting it away.

So, high, but within tolerence tyre pressure for a rim can turn into a pressure that is far too high for a rim that is starting to soften due to heat.

What happens I hear you ask?

Typically, our hero is descending a steep hill, on the brakes a lot, when the rim either deforms outward dramatically, sometimes locking the wheel, or simply spits the tyre off, both of these under brakes.

If the carbon is an insulator. How is it going to warm up properly?

Youre looking at hitting 180-200C throughout the bead to soften the epoxy.

The heat build up thing is purely a surface factor. Which might well ruin your braking. But it would take a lot of heat to soften the rim.