It is unlikely that you need the RST pin, but it is worth trying
U8G2_ST75256_JLX25664_1_HW_I2C u8g2(U8G2_R0, /* reset=*/ 8);
and connecting LCD_RST to digital#8 on your Nano33 IOT
The Wiki explains what 2ND_HW_I2C means e.g. https://github.com/olikraus/u8g2/wiki/u8g2setupcpp#communication
And it shows available constructors for ST75256 displays e.g. https://github.com/olikraus/u8g2/wiki/u8g2setupcpp#st75256-jlx25664-1
Yes, you need #define U8G2_16BIT because the display is 256 pixels wide.
As I said in #5 your wiring looks correct.
I would expect an I2C scanner to show 0x3C
I would expect the U8g2 examples to work even if the geometry is slightly wrong e.g. 256x64 driver on 256x96 hardware.
Regarding trans-reflective. "black text on white background" implies sunlight readability.
Obviously you need the backlight for night-time.
However sometimes it shows "better" with a backlight even in day-time.
The "white text on blue background" require backlight at all times. And don't look that nice at any time.