Will not turn on

The battery needs to offer a bit of charge to enable the charging logic. So a flat battery won't allow the battery to charge.

A good way to think this is an old fashioned water pump needs to have water poured into it to create the needed vacuum seal the flap so it can pull up the water, without any water you can't get the pump to pump!

There is also a bit of circuitry which monitors the battery from over voltage and temp to prevent over charging the lithium battery to a point of failure. But that's not the issue here.

You might be able to get a bit of charge into the battery using a bench Power Supply, that's assuming the battery is still good. Otherwise you need a new battery MacBook Pro 16" 2023 Battery Replacement so far iFixit hasn't started stocking them as the need is so little here's one source laptopbatterydirect Replacement Battery for Apple A2780 (94.4Wh, 6 cells) I haven't used them so use care in ordering. The other option which is just wacky! Is replacing to entire uppercase. Apple finally made replacing the battery easy and yet they don't sell it directly!