"Is there a way to force Trisquel to analyse and write to a blank DVD-R"
Not if the drive doesn't physically support it. That's what the output of your command is showing. It's answering the question of "What are the *drive's* capabilities?" Not "What are Trisquel's capabilities" :)
If you want to see "yes" to these questions below... Writing.... Can write CD-RW : Yes Can write DVD-R : No Can write DVD-RAM : No Can write DVD-RW : No Can write DVD+RW : No ...then you will need a different drive.
