For the record, you have the i5-7267U, which I think is the 2020 model. The 2021 model is the one with the i5-8529U.
How the keyboard works is determined by the keyboard controller (KBC), a part of the embedded controller (EC). You have version CH-EC-V1.1.4 of the EC firmware. Seems there is a newer version CH-EC-V1.1.7 around, along with a matching BIOS version JXX-14-WU133SR200-V1.1.7. There exists also another version CH-EC-V1.8.0, which might be an even more recent update. Or it might be for a different hardware (depending on the serial #). Not sure.
I only know this from searching around when shopping for my CoreBook X, no direct experience with any of this, since the i5-8259U version I got has completely different firmware.
Somewhere on this forum there is a thread that someone got an updated EC firmware version 1.1.7 by contacting service@chuwi.com, and it fixed this problem. Then there was also someone else who bricked his laptop flashing the same EC firmware, since the hardware was not compatible. I think this update was described as applying to units “before 20105000”, whatever that means (I think it’s the serial # or part of it).
So I’d suggest contacting Chuwi service by e-mail, giving them your full serial #, and asking for a firmware update to fix this. Whatever they send you should be safe to use. Alternatively, you can also probably find the update file somewhere but not being certain it applies to your unit runs the risk of bricking the laptop if it doesn’t.
Alternatively, you can also remap some of the Fn keys with a utility such as SharpKeys. (Or by editing the value for Scancode Map under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layout in the Windows Registry.) This is not dangerous, since you can always just delete the value to go back to the default settings anytime. (I used this trick to rearrange the PgUp/PgDn/End keys.)