After upgrading the microcontroller to the STM32L031F6P6, I realized a very unfortunate fact.
Although the STM32L011F4P6 had the BOOT0 pin shared with the PB9 input, the new chip has only BOOT0 on this pin. Therefore, a press on the power button would not be detected. Although the design can still work with 2 buttons, I would like to have 3 buttons design.
On another note, ST also sells modules that includes both MCU and Bluetooth functionality, and if I can make is simpler that way, I will.
Next update in ... I don't really know...