That's just a generic USPS message that says your package has been delayed.

Generic could mean they didn't bother with the actual reason, or that it's a system-generated message. The system sees expected package delivery date and that it wasn't delivered at that time, so it generates an auto message (however this particular one doesn't seem to be a standard message).

The reason could be anything - too much mail so they're slow in getting all of them out, weather-related delay, some USPS truck had an accident, mailman quit/fired, etc.

Oct-Dec is peak mail time, so it's not a surprise some items are getting delayed. In fact USPS just raised package rates for this period.
https://about.usps.com/newsroom/national-releases/2021/0810-usps-announces-proposed-temporary-rate-adjustments-for-2021-peak-holiday-season.htm

Long story short, you will likely get your package, it's just delayed.