I know many people are reporting the clock time is not correct on 2021 Infiniti's (QX50) and the SET CLOCK MANUALLY is grayed out. This is how I fixed the issue. Go to your Sirius/XM setting and select EDIT WEATHER/LOCATION. Select your location from the menu. Once your area is selected, you can then go to the main menu, select clock and you should be able to enter your time/date, etc.
This worked for me, I hope it works for you.