Converting Dolby Vision to HDR10

[fcs001fcs]

I tried using the updated command in the first post of this thread, but I am in the Exec Console of a Jellyfin Container in Portainer on a Terramaster F4-423 NAS and I get the below error.

Code:

[out#0/matroska @ 0x560aec387200] Error opening output /movies/XXXXTest/hdr10_video.mkv: Read-only file system
Error opening output file /movies/XXXXTest/hdr10_video.mkv.
Error opening output files: Read-only file system

I tried logging in as root and then the PUID:GUID, but the same thing.

How can I get this to work?