I now consider the wiring definitive.
SDA to GPIO10 (i2c1)
SCL to GPIO11 (i2c1)
3V3 and GND taken from extra headers soldered on the keypad base.
Default wiring, no change
GPIO 16 (LCD_DC) and GPIO 20 (BL_EN) unchanged
Reset unchanged, as 3V3 and GND
LCD_CS connected to GPIO 21
LCD_SCLK to GPIO 26 (SPI1)
LCD_MOSI to GPIO 27 (SPI1)
Buttons and RGB lines, that are on the opposite row can be wired as intended: they are not used by anything else.
Here is a preview of what it now looks like
*Update 2021-03-22. Fix wiring.