if an android phone is encrypted, will any new apps or data installed or added to phone after encryption also be encrypted?
Android 6 used Android Open Source Project: Full Disk Encryption
Full-disk encryption uses a single key—protected with the user’s device password—to protect the whole of a device’s userdata partition. Upon boot, the user must provide their credentials before any part of the disk is accessible.
So all apps & data installed on the userdata disk partition would be secured by that key. One way to think of
Full Disk Encryption is like a exterior door house key, once you can get into the house, the contents are accessible.