[Device Reviews and Information] bitbang3r:
Well, for what it's worth, I managed to fix the problem. I reinstalled Windows 10 yet again from the flash drive (to no avail), then did the following:

1. Got into Device Manager entirely via keyboard, with the mouse pointer going nuts. Yeah, it was fun. From what I vaguely remember, using a USB keyboard, I launched the search box using the Windows key, searched for "Device Manager" (sans quotes), then used tab & cursor to make my way to Human Interface Devices -> Goodix Touch Driver.

2. I deleted the device. Important! Don't check the box to delete the driver files, as satisfying as it might seem.

3. I fought with Windows for a while, because it kept spontaneously re-detecting the device and reinstalling it. I think the problem was that as long as Device Manager was active, it was periodically re-scanning for unknown devices. All I know is that eventually, I managed to kill the touchscreen driver & got it to "stay dead". Once the touchscreen driver was killed, I was able to use a USB mouse normally and continue with step 4.

4. I went to http://techtablets.com/chuwi-hi12/downloads, expanded "Windows Drivers", downloaded the one labeled as "TouchSetting To Fix Missed Touches", extracted the files in the .zip, then copied TouchSetting.gt to c:\windows\inf (you'll have to give admin permission to do it) and rebooted. It worked!

4a. Ok, I lied. Before I succeeded with step 4, I tried the one that was labeled "Hi12 TouchSetting Original Place in Windows INF" (which was also a file named TouchSetting.gt), copied it to c:\windows\inf, and rebooted. That didn't work. I have no idea whether it was just a case of Windows wackiness, or whether the file mentioned in this step is genuinely bad & the "missed touches" one was good. Either way, step 4 did fix the problem.

If you get a message from Google Drive saying that "too many people have tried to download the file", try using a different computer, or try later. I actually got the "too many people" message when I tried retracing my steps to document them for this update. Assuming you're reading this shortly after July 1, 2020, the link IS probably going to work eventually if you keep trying. Regardless, I'd strongly recommend grabbing copies of ALL the files you see at the link above & saving them in perpetuity, along with hoarded copies of every OTHER Hi12-related file you stumble across. The degree of link rot with this tablet is positively unreal, made a thousand times worse by the fact that its own manufacturer doesn't seem to care enough to host its own copies of the drivers for their own products. :(

Update: since the file that fixed it is text, short, and so hard to find (I actually attempted about 7 or 8 different "TouchSetting.gt" files, downloaded from multiple places before finally stumbling over one that worked), I'm just going to paste it here for future reference. To use it, just paste it into a file named "TouchSetting.gt", then copy it to c:\windows\inf

[Setting]
;UpdateCFG=0
SendCFG=1	;Send CFG to touch IC when loading driver
SleepDisable=0
PhysicalXsize=3072	;Physical size£¬the unit is 0.1mm
PhysicalYsize=1800

[Support]
ESD=1	;Driver supports ESD recovery processing
;SensorID=0	;According to the different SensorID send different configuration
GtpTool=0	;GuitarTestPlateform tool support
X2X=0
Y2Y=0
X2Y=0
Log=0
Flashless=0
ICType=GT910
PrtScreen=0
CtrlAltDel=0
HomeKeyTouchTime=1
VolumeKeyEnable=0
FingerFirst=0
PenAsFinger=0
resetRevert=0

[Feature]
Pen=1	;stylus/pen support
NumberOfKey=1	;The total number of keys supported,equal to 0 does not support key
Key1=0xe3	;0xe3 is home key,Must be a hexadecimal number
Key2=
Key3=
Key4=

[CFG]
;--------- 8047 8048 8049 804A 804B 804C 804D 804E 804F 8050 8051 8052 8053 8054
DefaultCFG=0x00,0x70,0x08,0x78,0x05,0x0A,0x7D,0x01,0x01,0x01,0x19,0x0F,0x41,0x32,0x03,0x05,0x00,0x00,0x00,0x00,0x12,0x23,0x00,0x18,0x1A,0x1E,0x14,0x95,0x35,0xFF,0x38,0x3A,0x12,0x0C,0x00,0x00,0x00,0x21,0x03,0x1D,0x16,0x18,0x1A,0xA0,0x82,0x03,0x41,0x28,0x1E,0x00,0x00,0x31,0x4F,0x94,0xD5,0x02,0x08,0x00,0x00,0x04,0x8F,0x33,0x00,0x88,0x38,0x00,0x7F,0x3E,0x00,0x79,0x44,0x00,0x73,0x4B,0x00,0x73,0x80,0x00,0x00,0x00,0xF0,0x4A,0x3A,0xFF,0xFF,0x27,0xFF,0x00,0x00,0x4A,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E,0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,0x1A,0x1B,0x1C,0x1D,0x2A,0x29,0x28,0x27,0x26,0x25,0x24,0x23,0x22,0x21,0x20,0x1F,0x1E,0x1D,0x1C,0x1B,0x19,0x18,0x17,0x16,0x15,0x14,0x13,0x12,0x11,0x10,0x0F,0x0E,0x0D,0x0C,0x0B,0x0A,0x09,0x08,0x07,0x06,0x05,0x04,0x03,0x02,0x01,0x00,0x111,0x01
;DefaultCFG=0x00,0x70,0x08,0x78,0x05,0x0A,0x7D,0x01,0x01,0x08,0x19,0x0F,0x64,0x3C,0x03,0x05,0x00,0x00,0x00,0x00,0x12,0x23,0x00,0x18,0x1A,0x1E,0x14,0x95,0x35,0xFF,0x38,0x3A,0x12,0x0C,0x00,0x00,0x00,0x21,0x03,0x1D,0x16,0x18,0x1A,0xA0,0x82,0x03,0x41,0x28,0x1E,0x00,0x00,0x31,0x4F,0x94,0xD5,0x02,0x08,0x00,0x00,0x04,0x8F,0x33,0x00,0x88,0x38,0x00,0x7F,0x3E,0x00,0x79,0x44,0x00,0x73,0x4B,0x00,0x73,0x80,0x00,0x00,0x00,0xF0,0x4A,0x3A,0xFF,0xFF,0x27,0xFF,0x00,0x00,0x4A,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E,0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,0x1A,0x1B,0x1C,0x1D,0x2A,0x29,0x28,0x27,0x26,0x25,0x24,0x23,0x22,0x21,0x20,0x1F,0x1E,0x1D,0x1C,0x1B,0x19,0x18,0x17,0x16,0x15,0x14,0x13,0x12,0x11,0x10,0x0F,0x0E,0x0D,0x0C,0x0B,0x0A,0x09,0x08,0x07,0x06,0x05,0x04,0x03,0x02,0x01,0x00,0xDD,0x01
;DefaultCFG=0x00,0x80,0x07,0x38,0x04,0x0A,0x7D,0x41,0x01,0x03,0x50,0x0F,0x41,0x32,0x03,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x18,0x1A,0x1E,0x14,0x95,0x15,0xFF,0x17,0x15,0xA6,0x22,0x00,0x00,0x00,0x84,0x03,0x1D,0x00,0x00,0x00,0x80,0x82,0x02,0x1E,0x23,0x14,0x0F,0x00,0x0F,0x23,0x94,0xC5,0x02,0x07,0x00,0x00,0x04,0xA0,0x10,0x00,0x8F,0x13,0x00,0x83,0x16,0x00,0x75,0x1B,0x00,0x6D,0x20,0x00,0x6D,0xF0,0x00,0x00,0x00,0x23,0xF0,0xB0,0xFF,0xFF,0x27,0x00,0x00,0x00,0x0F,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x1D,0x1C,0x1B,0x1A,0x19,0x18,0x17,0x16,0x15,0x14,0x13,0x12,0x11,0x10,0x0F,0x0E,0x0D,0x0C,0x0B,0x0A,0x09,0x08,0x07,0x06,0x05,0x04,0x03,0x02,0x01,0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E,0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,0x1B,0x1C,0x1D,0x1E,0x1F,0x20,0x21,0x22,0x23,0x24,0x25,0x26,0x27,0x28,0x29,0x2A,0x00,0x76,0x01

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