The App does not allow synchronization by deleting the uploaded files

Hello again!!!
Nextcloud running on a Raspberry Pi and synchronizing my Android with a USB hard disk connected to the Raspi. Nextcloud by Docker.
On my smartphone I have an SD card with my photos synchronized with Nextcloud, using the App.

In the past everything worked perfectly and it allowed me that the uploaded files were deleted from the SD card once synced.
However, I changed the sd card, which forced me to completely reinstall Nextcloud (both the server part and the App, after deleting all the App and PC data).
The problem is that in this new installation, it does not allow me to synchronize by deleting the uploaded files, it tells me that they are read-only.
I have verified that the files on the SD card (which are copies of the previous ones by “rsync -a”) are actually read and write, and I don’t understand why it won’t let me delete them by Nextcloud.
I have done an SSH to the phone to see the properties of the files, and this is what I have:


As you can see, there are read and write permissions for the owner, and only read for the group. Is it possible that the problem comes from this issue?
Really, managing permissions in Android is complicated and I find it inconvenient, so I understand that there must be another simpler solution.

Thank you very much again!!!