I have a similar issue with my cheap tws earbuds. What i ended up doing was cleaning up the metal contacts on both the earbuds and the case. And whenever i place my earbuds in my case i give it a little wiggle just to make sure the metal contacts are actually touching. I have no clue if this will help or whether pixel buds even have such metal contacts but you can try.
USB stick should work just fine. If you scroll down on the instructions a bit it says insert your usb drive 8gigs or larger to flash Ubuntu onto.