there are more official maps in the challanges folder aside from the campaign, but I'd like to be able to select them like the other tracks. I know there is a way to do this in TM ESWC where you can make the bonus tracks appear by replacing the Nadeo folder with an altered version, and I wondered if somebody had created a similar one for TM Sunrise.

I'm not sure about adding them to the nadeo campaign, but you can add the bonus tracks as a custom campaign. I added all the bonus tracks in 4 series inside a custom campaign, mirroring how they look in the track folders. You can see what it looks like in this run: https://www.speedrun.com/tmsex/run/yv9qwj8z

When I have some free time, I could check if this custom campaign can be easily shared or downloadable.

Thank you, this solved my problem. Creating my own custom campaign with the bonus tracks is sufficient for me.