lovefromisrael the shop told me there is no warranty if i install a different system..
This isn't true. Google Pixel devices specifically allow you to install alternative operating systems, so that won't void your warranty. You are just using the phone as intended, so they are still legally obligated to provide warranty service.
It might void your warranty if you do it on other phones where it isn't allowed, as then you have used the phone in ways the manufacturer didn't intend.
trashaccount hold down the power button for more than 2 minutes.
Just curious, what does this do? What is magical with holding it for a longer time?