Complete failure to install

[TheDreadPirate]

file inaccessible

common causes
service is already installed and running
user does not have permission to access the destination
destination does not exist therefor destination is not accessible

potential fixes;
check services to see if jellyfin is running
open the file location in file explorer
check if file exists, if exists attempt to delete; on failure to delete investigate
check file permissions
check location permissions

alternative; install to different location (if not already installed)

I second the idea that Jellyfin is still running.  Make sure there aren't any zombie jellyfin.exe processes in Task Manager.