Files and photos can be backed up multiple ways. You could connect a USB flash drive, upload to the cloud, or transfer them using Nearby Share or other wireless file transfer app.
SMS can be backed up using apps such as SMS Backup & Restore (by Synctech) or Super Backup and Restore. I don’t know if these apps also work for RCS chats though.
App data is the hardest. If it doesn’t connect to the cloud (like games) or have a native backup method then you would have to hope the Google backup works for it or try ADB backup (again this won’t work for every app).