Corelz125 Interesting puzzles there. Cutting that square out is a challenge.
I've printed out a cutting template on self adhesive A4 paper which will need to be adjusted for the thickness of the timber (green dotted through red rectangles), (the red arrows indicate grain direction and up orientation). Simply cut the rectangle perimeter and then cut out the inside. I'm hoping to try the cutout on the bandsaw using the fence and a 6.35mm blade... unfortunately its drinkSaturday night so, testing may be postponed for awhile.
If this works, it should be simple to make using conventional tools... unless one can scroll straight, which should be a laydown misere.
If your first cut is too short... Take the second cut from the longer end... LBD