But you can install whatever FOSS you want, as long as you can figure it out or find it on App Store. Not providing easy way to do it outside of their platform is not the same as not allowing it.

People are framing the argument against App Store as if they are blocking people from installing software into the devices they bought. Probably this attracts more sympathy but the reality is different, what Apple restricts is the access to its software distribution platform. That's why it's not the users that are pissed off but the developers.

Apple is not selling the right to install software to your iDevice, that's the developers who sell the right to install the software they created. Apple sells the right to distribute software to the devices they make, it's called Apple Developer Program and that's the one that costs money and has restrictions.