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

Hi Robin,
that was a good advice for me with the blank line and also the tutorial with the buttons. I found that what I think. The button has no function for the µP.

digitalRead(BTN) <--no pressing the button
=0
digitalRead(BTN) <--Here I pressed the button
=0
digitalRead(B4) <--no pressing the button
=0
digitalRead(B4) <--Here I pressed the button
=1

The extension button works fine like in the tutorial but not the BTN. That's why I can not do the Update, but what is the cause?