Arduino for STM32

Nucleo F334R8 have not been added only the generic F334R8 is available.
You can use it and redefine some of the generic definintion (LED_BUILTIN, Serial RX/TX, Clock config...)

Well hard to help, probably one ore more packages not properly installed. Or if you made a new install the IDE cache prevents to fix the issue.
You should try to properly removed all cache files form the ide.

Those function are not available within the Roger's core only with STM32 core.
I don't have in mind how to properly reset the MCU but guess someone have the answer.

I've built your code for STM32G030F6P and have no error.
I guess you didn't select the correct board part number in the menu and you build for AGAFIA_SG0 which does not have PC15

Hi, the log is enough clear that the code can't fit to the Flash nor the RAM. Unfortunately, depending of the mcu you used, the one with small flash and/or RAM require to do some customization. Ex: https://github.com/stm32duino/Arduino_Core_STM32/wiki/HAL-configuration#example-of-blinkino-for-nucleo...

Here

Right. Anyway using arduino cli avoid issue. It have to be in the path to be used by cmake.

Normally step 5 is enough. 6 and 7 are not properly managed by IDE.

You need to build with optimize for debug selected in the menu. A STlink with reset signal connected.

This is an Arduino IDE issue. Maybe some configuration could help.