Hello the google playstore has set some requirements for the target sdk that it should target at least api 26. I would like to know if it is compulsory for all apps to be hosted on the playstore to be built with the api 26 or is it just the target version in the Android manifest that should be API 26
Well technically it's just the target SDK that needs to be 26 or later, but you can't really make a project with a compile SDK lower than the target. Android Studio will warn you and might not even let you compile.
Even if it does, why? You don't get around runtime permissions by compiling with SDK 22 if you target 23. You don't avoid the Settings.System write restrictions either. The target SDK is the important one.