Diagnosis
The USB-C port does support up to 65W Power Delivery, but it's not a simple pass-through. It needs to be the primary video input for the power negotiation to work correctly.
How to Fix It
Make sure you are using the USB-C port for both video AND data. Connect your laptop directly to the monitor's USB-C port with a certified USB-C cable that supports video and PD (like the one that may have come with your laptop). The monitor must be set to the USB-C input. You can't have video coming from HDMI and expect power from USB-C. Also, check the OSD: Go to 'Setup' -> 'USB-C Power' and ensure it's set to 'On' (it should be by default).
If That Didn't Work
Your laptop might require more than 65W to charge under load. Check its power adapter rating. If it needs 90W or 100W, the 65W from the monitor will only slow-drain or maintain the battery during light use, not charge it quickly.
Heads Up
The USB-C port shares bandwidth. If you have the USB-B upstream cable connected to your PC for the hub, the USB-C port's data speed drops. For full function, you typically choose one upstream connection: USB-B to your desktop PC for the hub, or USB-C directly to a laptop for a single-cable setup.