Nothing in that graph indicates a “99% Biden” vote dump. The steep vertical line you see in blue is painting over another steep vertical line in red, indicating

Nothing in that graph indicates a “99% Biden” vote dump. The steep vertical line you see in blue is painting over another steep vertical line in red, indicating trump also got a significant number of votes in that dump (although much less then Biden. I’d estimate something like 75% Biden from eyeballing it). If it was a 99% dump, the red line would be seen continuing on its original path to the right.