Android 11: How to add an icon to the home screen that will lock the screen?

nope

sorry

 

YES!

Greenify has this option.
https://greenify.en.uptodown.com/android

There are even two different ways it can be done, an icon or a long press on the home button.

 

Also, if you prefer, there are apps that can lock the screen when the proximity sensor is covered for a set length of time.

https://f-droid.org/en/packages/com.jarsilio.android.waveup/

 

I use both of the apps I suggested on all of my devices, because I do not like using the power button either.

 

Tasker offers two locking options, the regular system lock, or taskers own lock, which will present a number pad to unlock. You can activate either lock in any of a number of ways, I do it it with a left - right shake of the phone.