My MacBook Air 2019 doesn't charge when its OFF

Newer versions of macOS battery health management works a bit different.

macOS determines when to charge and not to charge.

I wouldn't worry about it as long as condition of battery is stated as"Normal".

For details: https://support.apple.com/en-us/HT211094

For additional help:

https://support.apple.com/guide/mac-help/if-your-battery-status-is-not-charging-mh20876/mac

https://support.apple.com/en-asia/guide/mac-help/mh29198/mac

• Normal: The battery is functioning normally. 

https://support.apple.com/en-sg/HT204054

New Battery Health Management system is trying to learn a user's battery usage pattern.

When it has sufficient data, it is supposed to alter the charging pattern.

Until then, let macOS do its job.

I am also seeing variations in the behavior.

Condition: Normal is the critical thing to watch.

Keep an eye on it.

To follow on what @dominic23 has already explained another article to read about charging the battery. If battery charging is paused or on hold on your Mac