Lukewarm. I’m not sure what causes it but it tends to shrink them quite badly.
If the clothes aren't moving well enough for them or air to move around, heat pockets can easily lead to shrinkage (or 'cigarette burn' holes in high-polyester shirts).
The scenario where after one long round some of your stuff is dry (or even shrunk/damaged) but others are still damp? Probably a sign of an overload or bad load (e.x. comforters + anything but MAYBE sheets tends to be a bad idea...) Or your socks were still balled from the washer and they should be unballed and rewashed b/c they are probably not that clean.
If you are overloading a dryer, I've found it best take some clothes out and -not- overload it if you can. I had a very 'consistent' clothing load and a lot of free time during covid, and more or less 'found' that with my dryer, splitting an overload into two normal loads takes about as long as
If you -can't-, try to do as many of these as you can:
1. Do -not- try to bump up the temp to overcompensate for the load size. If anything you may want to prefer a lower temperature.
2. Prefer shorter 'rounds' of 20-30 minutes, and manually 'rotate/redistribute' the clothing between each round. This way if the clothes aren't tumbling, you are at least making sure there's some rotation. Ideally you're able to get to the thing within a minute or two to check the rotation and re-start to keep this semi energy efficient... This is a bit easier if you're at a 'laundromat' or have laundry as part of a weekend cleaning routine or whatever. The good thing is, this will probably help the overall load finish faster regardless.
3. Per the comment about the socks... have some mindfulness in transferring the overload. At least in the US it likely means the washer overloaded too (I know other countries may have smaller driers vs washers etc), and I have seen plenty of washes where one of two pieces of clothing just didn't have anywhere to let the water out during the spin. Leave those in the washer till you transfer the others, then try to get the water out. Don't wring the clothing, but consider gently pressing it (for a T-shirt, 'foliding' it and a squeeze over the washer basin will do the job as long as you're gentle about it, or you can 'press' it against, or just run it on a spin or in the next load.)