AB19 I was just looking at the calendar and realized the paycheck coming 12/29 is the one for PP 26-2020 which ends on 12/19, so even if the government does shut down, worst-case we'll get nine out of ten days' worth of pay on that paycheck—PP 01-2021 doesn't start until 12/20. I certainly hope 90% of your paycheck is enough to cover TSP contributions, etc, so it looks like we're out of the woods on that.
This is assuming payroll is able to process the paycheck properly, which is what people say on reddit. We should get an LES and direct deposit as normal and on time for all days worked up through 12/18 because the government actually has funding for those days. We won't get paid for 12/19 or later until the shutdown ends. That's what I've seen people say.