I'm going to describe something I've been through with the STM32 and the Arduino platform since I started using it a few years ago. Maybe it can help someone in the future not to waste too much time.
I've already tried using Arduino IDE with STM32, it's interesting for simple things that are already implemented, but the user has to use it the way it is. If the user need to modify something, it is more recommended to use HAL with STM32CubeIDE. Although it is a bit difficult to learn to use a new IDE, over time it is the best alternative to get the best performance from STM32, the next step is to use baremetal code (register manipulation) which can be easier with STM32CubeIDE.
The new Arduino IDE version 2 helped with code navigation, but even so the integration with the STM32 peripherals is done little by little by the developers of the libraries, in the STM32CubeIDE almost everything is already implemented.
The Arduino platform uses a layer of code independence in relation to the hardware, perhaps comparable to CMSIS (Common Microcontroller Software Interface Standard) so when the STM32 hardware user asks for help on the Arduino forum, few people will be able to have the knowledge to help. Something similar happens when the Arduino IDE user seeks help on the ST forum, few people are aware of the adaptations that were made to the STM32Cube codes to serve the Arduino platform.
Regarding the use of the UART, it is not very complicated to use, the user have to do the initializations, which can be the most difficult part for an Arduino IDE user, whereas in the STM32CubeIDE this must be done automatically with the help of the visual configurator (Device Configuration Tool Code Generator).
The examples for other lines of STM32 can serve as a basis to help the user understand how to implement:
https://wiki.st.com/stm32mcu/wiki/STM32StepByStep:Step3_Introduction_to_the_UART
