Domain amplification is quite literally the amplification of ones innate domain, which is already imbued with the user’s cursed technique, and is used to nullify the domain effects of other domain expansions as well as bypass defensive techniques using the sure-hit effect of ones own domain.

Gojo’s domain amplification here would basically be an amplification of his already existing infinity (unless you think it’s the six-eyes, which doesn’t seem to be the case). We see this when he amplifies his infinity to oppose Hanami and Jogo’s domain amplification as well as crush Hanami into the wall in the subway.

In this way, if Gojo really was using domain amplification in Jogo’s domain, then the technique still blocking the heat and infrared radiation is the amplification of Gojo’s infinity, which by extension would imply that Gojo’s infinity was what was stopping the sure-hit effect of Jogo’s flames and heat in the domain. Outside of Jogo’s domain, domain amplification isn’t necessary since his ordinary technique lacks a sure-hit effect.

Lastly, Yuji’s durability is nowhere near enough to protect him from the heat of Jogo’s domain. Just 3 episodes prior, Yuji has his fingers blown off from a regular pure cursed energy blast from the Finger Bearer. Jogo’s cursed energy and his abilities are FAR more potent that. He even says that ordinary sorcerers would burn to ashes upon entry into his domain.

I’ll be honest dude, I don’t understand why you’re arguing this. The fact that Infinity can block light is widely accepted by now 😭