Thanks for the reply!
As I said, I will not venture to install Nextcloud myself because I am a beginner in linux and I do not like to ruin things. Now I use an older version of ReadyCLOUD installed on my phone and it works almost well but I wish I could use Nextcloud installed on my R7800...
Thank you very much and I appreciate your answer! But linux is not my strong point. Maybe someone who knows how to do this will develop this idea.
However, I was able to back up my photos by installing an older version of Readycloud (2.0.4) on my phone.
I use Voxel firmware and kmoj v5. I searched but couldn't find how to install nexcloud or another backup method on my R7800 router. Readycloud does not back up my phone and I decided to use another method. Can someone help me?