What about if i have Ubuntu with Bitcoin core in the PPA? its auto updating it, i dont do anything manually beside clicking on Update

You do the same for your core system: just click to update. It could even be set to auto-update.
If you can't trust the Bitcoin core in there, you can't trust the rest of your system. And if you can't trust the rest of your system, not only Bitcoin but also your online banking could be compromised.
So far I trust my operating system, and it's almost impossible for me to check if it's compromised anyway.