It's said high voltage will stress battery and wear it out in the long run?

Batteries are designed to last about 2-4 years on average- half may go longer, but half will go less than that.

Think of charging as a unit, rather than a percentage.
If you only charge your device to 80% or so, then you are screwing yourself out of potential charge life, which means that you will need to charge more often.

Batteries and devices both have voltage and heat sensors to prevent damage to the battery.
(Yes, techically higher charge voltage and temperature can degrade batteries faster anyway, but they will still survive the prescribed amout of time.)

When you charge a battery from 0% up to 100%, that would be one full charge unit.
If it was 50% up to 100% then that is half a charge unit.

So you could do that twice and it would be the same as in the first case.

These batteries are designed to last a certain number of full charge units, generally typical use over 2-4 years.
No matter how you divide those units, the total remains unchanged.

So you are only annoying yourself and not allowing full potential of your battery if you never complete a charge.

Probably the two worst things are heat and charging from completely dead.
Avoid these two things if at all possible.

The rest is useless worry created by people that need to write junk.

 

To answer your other questions:

All batteries degrade over time.
This is independent of any use or none at all.
The battery is a chemical reaction that begins the moment the battery is created.
This chemical reaction eventually will cease, like all chemical reactions do.

 

https://www.androidauthority.com/smartphone-battery-life-drain-causes-1071423/

 

battery university is my go to for all things on lithium-ion batteries.

it can get pretty scientific in terminology but it really gives you a great break down about batteries, how they work and how to charge them properly.

https://batteryuniversity.com/article/understanding-lithium-ion

 

FWIW Google did introduce charging limits with Android 12, where the phone can be set to not charge above a certain amount. On my Galaxy Note20 Ultra, it's stop charging at 85%. I have enabled this, as I rarely use more than 40-50% in a single day with this phone. Although when I'm travelling, I do want to the phone to be charged 100% before I start out.