2021 Mazda CX5. Can only lock/unlock car manually. Tailgate doesn't open. No dashboard lights. Manual fob start doesn't work. Have had no battery warning lights but tried jump start with no luck. Mazda dealer not open on a Sunday. What's going on?

 

If all your breakers are good (I assume you checked them especially after attempting a jump) and your battery has any charge at all, or your FOB battery is dead, you should get warning lights.
You say you didn't get any of these, which leads me to believe your battery is completely dead.
You cannot jump start a completely dead/failed battery.
The FOB batteries don't last long I have already had to replace them in my 2020 CX-5.
The OEM battery was even worse, it only lasted a year.
I replaced it with a much better one.
My opinion based on the above, you need a new vehicle battery.

 

Agreed. Sounds like battery is toast...

 

1st step, try your spare remote.
2nd step, if needed replace the battery in your remote.