Hi, after update 13.6.1, power button stopped working? Any ideas to fix this

first see

Learn what to do if a button or switch isn't working.

If that does not help I would first make sure you have a backup so your data is saved then restore as new.

Here is a guide for those steps:

How to back up your iPhone, iPad, and iPod touch

Restore your iPhone, iPad, or iPod to factory settings

and see how it goes

If button not fixed then send it for repair or replace battery

If it works now restore from backup but be prepared to wipe again without restore from backup. 

https://support.apple.com/en-us/HT204184