Indeed, for a single app it might be a lot, considering it’s a single app. But even then it’s not a lot of disk space out of what people have. But with every additional app, that additional space use lessens thanks to shared runtimes and dedupping.

Also i don’t know what is flapak runtimes which are big and different versions of them are required for different apps

I think a few of the most used one cover most apps, but even with different runtime versions and I think even different runtimes, thanks to dedupping it should only use extra space for stuff that’s actually different between the two. Two instances of the same library in different runtimes would only use the space of one, afaik.