Sync files to android 10's sd card

[setan]

Hello,

I have an older android device that I have been using as an audio player.
It's internal storage is low so I put all my music on the SD card.

On newer Androids I can use Syncthing to sync to the sd card, but for android 10 it doesn't have support for rw access.
What I did mostly on KDE was was wipe everything and copy everything using Dolphin.

I know that this is bad for the SD card so I have tried mtpfs + rsync, but it just throws errors. I think this is caused by the space in "SD card".

I wonder what other options I do have that don't involve tearing through the flash memory lifespan.
Can anyone suggest something?