Hello everybody

So i heard people do this thing called palm muting and it sounds awesom I want to learn. I tried it with pick.

Downstrum is ok i can do it but whats with the up strum? Is it possible or is there a technique to up strum while palm muting or guitarist dont do that and im just dumb

The extra question is about tuning. When I tune my guitar. Sometimes the tuner show that the tune is almost half a tune higher than it should be.

When the guitar used or after used the strings stretch right so the tune should be lower not higher right? So why is it higher? Its just poking me why this happen