It doesn't use open weather unfortunately. It uses the Norwegian Meteorology Institute and their weather prediction is poor/entirely inaccurate for much of the world. I do wish open weather was an option especially since it's easy to get your own weather api key.
If you are super new to Linux I would suggest another distro besides Debian. Debian is great and I love it but it's not set up out of the gate for games and newer people in general. Distros like Mint, ZorinOS, Bazzite, and Pop!OS are. Those distros will come with nvidia drivers or help you set up. Bazzite in particular is set up for gaming out of the box, I think it comes with steam and lutris pre installed.
If you have steam installed as a system app then copy the .desktop file from /usr/share/applications/steam.desktop to your /home/yourusername/.local/share/applications. Once you have the .desktop file in local, edit the desktop file and go down to the first Exec= line and and the -silent switch at the end.
But what are the Chinese going to be able to do you? If you are an American living under the American government theres much more they could do to you, such as locking you up.
If you like the interface of the steam deck in desktop mode and you are most familiar with Ubuntu, you could try Kubuntu.. which is just Ubuntu with the KDE desktop environment like what the deck has. Theres also the KDE Fedora spin. If you do want to go the Arch route you could install EndeavourOS, which is practically arch with a little bit of hand holding to get you on your feet quickly - and to help you learn the ropes.
Yes you should, but you have take your data safety into your own hands. You cannot trust Google, Apple, and other big tech companies. That is not to say that these companies should get away with the things they do, there should be punishment.. but that is the reality.
You could theme everything else vintage steam green... except Steam, Lol! That color does bring back memories of the good ol days of the internet and online gaming.
Edit: hold up, theres a secret Rick roll in there!
True, kind of silly you have to install an extension because the default gnome weather won't just let you use open weather.