As described, your issue has one of two potential causes.
First, you need to understand that all Apple devices that feature a USB-C port for charging the device support USB PD (Power Delivery). Other proprietary charging standards, such as QC (Quick Charge) are not supported.
The two potential causes for charging issues are:
1) If the Power Adapter that you are using at home does not explicitly support USB PD, it may not be suitable for charging Apple devices. NB: All Apple USB-C Power Adapters support USB PD.
2) If using a PD compliant Power Adapter or PowerBank to charge the iPad via USB-C, failure to charge when using either would suggest that (a) the iPad's charge controller has a fault, or (b) the USB-C cable used for charging is itself defective.
USB PD is an active protocol, in which the compliant power source, cable and load (the iPad in this instance) mutually negotiate the power profile that will be used for charging. If the negotiation fails, either no charging will occur, or charging will default to the standard USB 5V charging standard. Troubleshooting generally requires substitution of the Power Adapter and cable for another known-good item.
Troubleshooting
In detail, most models of iPad require a Power Adapter rated at 12W (i.e., 2.4A @5V) or greater to reliably charge. 5W Power Adapters (1.0A @5V) intended for older models of iPhone are inadequate to charge an iPad; if the iPad charges at all, charging will be very slow. Recent models of iPad are generally supplied with a 20W USB-C Power Adapter.
Some third-party USB-C power adapters (and portable PowerBanks) may not support USB PD. Power Delivery mutually negotiates the charging voltage; the source, load and cable are all elements involved in the negotiation protocol. Unless the Power Adapter explicitly supports USB PD, it will almost certainly fail to charge the iPad; proprietary charging standards, such as QC (Quick Charge), are not supported.
Many computer USB ports also cannot source sufficient power to charge an iPad. Unless explicitly designed for charging connected devices, computer USB ports are typically limited to 0.5-1A @5V (i.e., 2.5-5.0W).
If you continue to experience difficulties when using an appropriate Power Adapter of 12W or greater, you might be best advised to seek assistance directly from from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively, you can initiate and manage your support cases from Apple devices using the excellent Apple Support App. If not already installed, the App can be downloaded from the App Store:
https://apps.apple.com/app/apple-support/id1130498044
You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to fully test and assess your iPad, Power Adapter and cable(s):
Genius Bar Reservation and Apple Support Options - Apple
