I’m just using an S9 (non plus) and I am in the USA too. Having ZERO luck trying to upgrade to Q. I also tried a few stock Android 10 ROMs from both sammobile and samfrew. I don’t know if any of them will work - looking at what’s available, it seems that they’re categorized by country and carrier? i.e. I see Vodafone, Orange, T-Mobile options for different EU regions, none for USA of course, because we’re using non-USA phones. Are we wasting our time trying to upgrade to Q in the USA? Stuck with the old OS?
When sideloading them with the latest TWRP, about 8-10 different ones (UK, NZ, etc.), even one with a build date of April 2020 as noted by @SuzieQ in this thread - none of them worked - every one threw a ‘zip file is corrupt’ error message in TWRP. I also tried copying the ROM file to the phone, and using the install function within TWRP, and had the same result.
I posted in the thread above too so if that needs to be merged or moved please feel free.