MP3 conversion method in iTunes no longer working

Hi there!

I've successfully converted my iTunes songs into mp3 format using the tutorial outlined here (https://support.apple.com/en-gb/HT204310), but it hasn't worked on my most recent downloads.

The option to convert to MP3 is now greyed out.

On the Import Settings screen, i noticed at the bottom that it mentions "These settings do not apply to songs downloaded from the iTunes Store". Not sure if this is a recent development...

Thanks in advance for your time and help, whoever may be able to help. :)