As thin as possible. The thickness of an average phone case is probably the max thickness you'd want.

Higher temperatures to charge over 80%? That's new to me. I'm not disagreeing that traditionally the advice to prevent charging to 100% was sound. But with modern software maximizing battery life, there is no longer a need. If anything any benefit is just negligible at this point.

Additionally iOS trickle charges when temps get too high and also after about 85%. Temps aren't an issue.

See my reply to the other commenter above. It's about cycle count and temperature, my friend. Not a battery getting "stressed" over 80%.

They actually do

They mention operating temperature as a critical component as well as how their batteries are rated for 500 cycles before hitting 80% residual capacity. You can use optimized battery charging if you wish as it slightly reduces cycle count by holding the phone at 80% before finishing the charge to 100% instead of allowing for small partial discharges at 100% which count towards your cycle count.

This is factually incorrect.

Lithium ion batteries do not have memory. They degrade based on cycle count and operating temperature.

Discharging from 100% to 0% imparts as much wear as two-half cycles, for example 80% to 30% twice.

Charge your device freely, it will optimize the rest.

Haven't had any issues. iPhone 14 Pro since launch day.