Not really intended to be Arduino-ki
I'm not sure STM have a coherent strategy with their "Arduino" compatibility
Yes, they do sort of support some Arduino things... to attract students. But not to attract design win decision makers.
ST et al pursue BIG design wins, leading to hundreds of $M in sales in the verticals, smartcards, etc. Arduino is just to get students to remember ST when they get an engineering job. A marketing expense. Like Apple does with donations to schools.
Go to one of the frequent ST hands-on seminars and get free boards. Or just buy some and learn. This a far different world than messing with too-cheap China stuff in hardware, and Arduino libraries that are all too often buggy and most always myopic about coexistence with other I/O software.
Most of this stuff is less than a sidewalk cafe lunch on the Champs-Élysées.