my son (not yet 14yo) has learnt to write a few games in Roblox

he's learnt Lua, object orientated programing client side/ server side distributed programing (and how to optimse the speed)

he's also learnt that the people who run the platform will screw you over in many different ways (he's learnt a few tricks to semi counter this)

he's learnt that advertising can be useless and costly,

learnt people are extremely fickle, there's a far amount of people who have money to throw around

learnt that doing good graphics is harder than it seems. (also learnt how to use blender)

also that game dynamics and subtile changes can have big real world changes to peoples experiances

also that UI and UX are important

also to train other (kids) how to program - for money

I'd say as a learning platform it has been fantastic, he's not made much real money, but has earned a far amount of robuks (platforms currency) that's he's spent in game