How can I use a USBC DisplayPort monitor with my 12” MacBook and charge at the same time?
If you intend to use the Asus MB169C+ while also charging your MacBook, you will need an adaptor, hub, dock, etc.

Here are some examples for you:


Hub+
Kadi Port
Arc Hub


NOTE: I have not used any of these personally - I have linked to them just to provide some examples of how you can achieve what you want. However, there are many products that will meet your needs varying from cheap to expensive.