if your new apartment doesnt have cable it will have dsl. So you just need a new router

Either you buy all the parts and build it yourself, wich is just connecting them all together and screwing them into the case. Or you buy a prebuild one wich will cost a few bucks more.

go onto your router settings and disable the 5ghz frequency band. See if that works

are the letters appearing for a certain key always the same? If so maybe you chose the wrong keyboard layout?

Im not familiar with google fiber but im guessing its not ftth? Since they say “up to”? also have you checked in taskmanager if any task are heavy on ethernet/wifi