say_something_man The files are not actually "shredded" in any sense from storage, the storage space is just marked as free when you delete the file. An attacker that has your encryption password and has disassembled your phone and uses advanced forensics can likely recover your files. There may also be thumbnail pictures and other metadata left that such advanced forensics can recover. But as long as you have rebooted your phone at least once since deleting the files, there should be no means to recover the files or log entries about them from the phone UI itself, so it is safe against an attacker that won't disassemble your phone.
To actually shred the content of the deleted files, you must delete the user profile the files were stored in. This will securely wipe the encryption keys used for encrypting filenames and file content, for both the files themselves and any thumbnails or similar metadata, such that not even knowing our password will help to recover. To also shred information about number of files, exact file sizes, approximate file name lengths and so on, you must factory default the whole device. This will securely wipe the device encryption key such data is stored as.
Installed apps are different, the only way to wipe information about their former presence is to factory default your device, since the apps themselves aren't stored in any user profile, only app data is.