There are numerous ways to automatically back up files from your Android device, but they usually rely on the cloud. If you want to handle everything in-house, DAEMON Sync might be exactly what you need. This app syncs files from your phone to a computer on the same WiFi network. Nothing is sent over the internet at all.
This app is made by the same team behind the classic DAEMON Tools disc image software. If you spent any amount of time screwing around with PC games in the 90s and 2000s, you probably used DAEMON Tools. It lets you mount just about any disc image as a virtual drive and emulate that pesky DRM junk. It still exists, but it's not as necessary these days. But enough about the past, this is about the present, and Disc Soft's new sync app.
The setup process for DAEMON Sync is fast—download the app, install the server on your computer, and enter a PIN code to tie the two together. There are no passwords or user accounts to worry about. By default, DAEMON Sync will send photos, videos, and screenshots to the server. It even keeps them in separate folders. You can also add custom folders on your device to sync any file you want. It's free and seems to work well, so give it a shot.