> Thanks to Zephyr.

That only gets you proper support for a couple vendors (Nordic, ST), everything else is a nightmare. Even with better-supported vendors, there are whole swaths of things that aren't properly supported and you need to directly call code from underlying vendor SDK to make things work. That bodge makes the whole project non-portable. Even some simple things like ADC DMA on ST F1 series..

Can't share your experience.

Sometimes stuff is missing. But that's implemented and upstreamed quickly.