I wanted to use STM32F103 instead Arduno Mega for a radio with TEF6686 (see details at https://nicuflorica.blogspot.com/2020/02/radio-cu-tef6686.html).
First, I tested classical sketch named i2_scanner but I received no device or error at all adresses beginning with 0x01.
I search on internet and I found an interesting article STM32 I2C SCANNER. Because informations from there are too much and must read carefully, I change directly Arduino mega with STM32F103. I saw logo info on display and than nothing. I realised STM32 send correctly i2c comands to device, ut not understand messages from any device. LCD1602 (or LCD2004) need just commands, so can be used.
I tested with LCD1602 powered from external 5V and STM32 board with 3.3V fron USB-FTDI interface or through USB using internal voltage regulator.
Schematic is as in article from https://controllerstech.com/i2c-lcd-in-stm32/
I made i2c LCD1602 drived by STM32F103C movie using STM32F103_i2c_LCD1602.ino sketch: