Can the 2021 MacBook Pro be charged through the Thunderbolt 4 port?

yes, PROVIDED:

You are using a USB-C Power Delivery power adapter that can actually provide power of enough Watts at the appropriate Voltage, Such as connecting a USB-C charge cable to the Apple provided power adapter.

¿Connect a car battery directly? No, not a chance.

Just for your additional information, there have been some sporadic reports that the Thunderbolt ports do not always seem capable of "walk and chew gum at the same time", (e.g., when connecting a display AND providing USB-C power delivery input power TO the MacBook Pro AND providing a USB hub with additional peripherals, the Mac gets confused and drops some items.)

If that is a smaller USB-C Power delivery power adapter, it could be pressed into service for a MacBook Pro.

Apple does not recommend a "too small" power adapter, instead suggesting you provide about 85 Watts for a 14-in, and 100 watts for a 16-in to both charge and run simultaneously. (140 Watts to fast charge the 16-in models.)

What has changed is that Apple has removed the dire warnings that this will damage your computer. Instead, they say too small a Power adapter may force the computer to work more slowly, especially if it cannot freely "borrow" additional power from the battery.

If you have not already encountered it, the Mac USB-C CHARGE cable looks just like a "real" USB data cable.

However, it has ONLY charge conductors and USB suitable for running a keyboard or mouse -- it has no high-speed USB capability whatsoever.

I am thinking of painting mine orange so as not to mistake it for a "real" data cable.