Suggestions for file sync / android backup / sharing software (nextcloud alternative)

Hello everyone,

Since my daughter was born I am searching for a solution to share pictures of our child with my wife and create a copy of each smartphones photos and other files (documents). At first I tried nextcloud, but there is a lot of overhead and the administration feels kind of complex for what I need.

Anyone else having some input on which software to use?

So my main goal is:

Software running on raspberry pi (preferable docker). Has abilities like shared folder where pictures and documents get uploaded from multiple users and can be viewed (collaboration editing is not needed). Automatically copy files from smartphone (android) to raspberry from selected folder for a simple redundancy.