I recently switched to Joplin after using Colornote for quite a while. Due to Colornote's lack of export features, the migration process was a pain. Additionally, I wanted to keep the creation and modification dates of my notes intact. So I ended up writing a script that takes care of all of that. Here it is, in case anybody ever wants to do something similar:
P.S. I'm loving the app. I tried it a few years back but never switched over. It's really matured since that time. Kudos to the devs!