What I love about links like this is that we see information being shared just for the love of it. This person has done a lot of work simply to share knowledge with the world about something they are passionate about. This is what great about the internet and is easily lost amongst all the commercial content.
You only have to put your finger somewhere in between two frets to get a particular note, so you can play more than the tiny handful of chords that can be played on something like a violin.
There are non-fretted guitars but they are rare, and I think early banjos were not fretted.
If you haven't heard them yet, you're in for a wild ride: https://www.youtube.com/@AnginePoitrine
I see your added frets, and raise "add frets on the fly using Lego":
https://www.youtube.com/watch?v=rPCEImSfCwc
* https://www.delta-harp.com/
* https://www.youtube.com/watch?v=IdUztFVwi3I
You only have to put your finger somewhere in between two frets to get a particular note, so you can play more than the tiny handful of chords that can be played on something like a violin.
There are non-fretted guitars but they are rare, and I think early banjos were not fretted.