In Subnautica 2, the Heat Tolerance Adaptation is a game mechanic that allows you to access a markedly different biome roughly 250 meters away from the Lifepod. Acquiring it is a fairly involved process, as it is a major progression mechanic.
This Subnautica 2 guide has every major step towards getting the Heat Tolerance Adaptation.
Processor Blueprint
Once you have acquired the Habitat Blueprint, head for the Old Habitat about 400m to the north. Dive to a depth of 55m to find an airlock leading to the Processor.
Sonic Resonator Blueprint
In this same location, you can get a hold of both parts of the Sonic Resonator: one on a sidetable near an airlock, and the other in an adjoining room, lying on the floor.
Silver Ore
You will be needing this precious resource for the process, and you can find it right near the Old Habitat, in a large cave.
Construct Processor
With 2 Titanium, 1 Mild Acid, and 1 Copper Wire, you are set to construct a Processor within a Habitat. Once done, configure your newly built Processor to load and process Titanium into Ingots.
Craft Sonic Resonator
The Titanium Ingots will allow you to finally craft a Sonic Resonator at the Fabricator.
Heat Tolerance Adaptation
Go south-west around 200m towards the Blackbox – Wander signal and find a tunnel leading straight down at a depth of 35 odd meters. Use your new Sonic Resonator to clear the bloom biofilm cankers that are obstructing your path through. Continue the process until you have successfully purged the infection.
Completely clearing the Angel Comb of its affliction and sampling its core is how you will finally acquire the Heat Tolerance Adaptation.
That is everything there is to know about unlocking the Heat Tolerance Adaptation in Subnautica 2.