Development tools for Zephyr on STM32Workbench for Zephyr: VS Code extension to set up, build, flash and debug Zephyr applications on STM32.Devicetree manager: browse, edit and visualize Zephyr devicetree, STM32CubeMX-like for Zephyr.
The problem is probably that the linker eliminates your code, thinking it's not used; try suppressing the weak definition for TIM6_DAC_IRQHandler in startup_stm32l053xx.s to see if it solves the problem.