My pico ist unable to activate the bootloader to upgrade the firmware 1.93 to 1.99

...too many cooks... but I give it a try again about the flashings and blinkings:

1. just inserting the PICO into USB makes PICO blink red briefly once - not in boot loader mode, not connected (yet), but connectable
   
2. inserting with button pressed and held into USB makes PICO pulse green and red alternately - in boot loader mode, not connected (yet), but connectable
   
3. uploading (and running) the line of code of post #3 turns the red LED on when pressing the button, and off, when button is released / not pressed (anymore).
   
   

#1. is used for checking if PICO is still alive (for the most part)
#2. is used to go into update of firmware - boot loader mode
#3. is used to test if button works and is recognized by PICO