I have come across multiple YT videos (about the new higher USB power delivery and battery degradation) mentioning that chargers communicate with the phone or laptop when charging to avoid battery degradation, or avoid supplying too high a power. Is that really true and is there some kind of standard for that? Do nearly all chargers support it?
Yes - modern devices absolutely negotiate what charge current they will accept, and what the charger can provide. In fact without negotiation, the device will only get 500 mA, which may not be enough to increase the battery charge while the unit is working hard.
Example: My work iphone can use power faster than my car charger can provide, noticeably when hotspotting.
Consider that an electric car charger is a big version of the phone charger, and that some of these ideas may trickle down into smaller hand-held items in the future.
The fancier chargers can negotiate with the attached device to calculate a mutually-agreeable charging current, and can even consider the time of day the car will be needed and can work out a slower charge that gets the battery to capacity before needed.
Some fancy multi-slot chargers can work out which devices are needed soonest, and prioritise charging them first, which is why some chargers ask when you will need the vehicle back.
Imagine if you had a phone/tablet charging alongside your electric hair trimmer that is only used once a week.
Finally, some cars can charge, and then tell the charger to keep providing power which is used to pre-heat the cabin rather than taking the power out of the batteries.
I've noticed my phone charges up in the early part of the night, and then bounces from 95% To 100% until morning. It would be fantastic if the phone could take power from the charger to run itself directly, and leave the battery at 100%.
USB-PD (power delivery) lets the phone communicate with a power supply to pick a voltage/current that both support. For example, a power supply might support 5, 9, 12 and 20V, but a phone might only support 5, 9 and 12v. Supplying the phone with 20V when it can only handle 12 could destroy it, so in reality USB-PD is there to protect your devices from destroying one another while still being able to use higher voltages when both devices are compatible.
USB-PD is just for negotiation of voltage/current. What the load does with that is its own business, so battery charging is not something the power supply knows about. The battery charge controller in the phone handles battery charging.
You will find the answer if you research "USB charge negotiation".
What you are calling "chargers" are power supplies. The charge controller is in the phone. The phone tries to communicate with the power supply to learn how much current it can safely draw. If it can't communicate it assumes 500 mA max.