https://scottishcastles.xyz/
Scottish Castles.xyz contains a zoomable map showing the location of every map in Scotland.
An interactive map of all castles in Scotland with links to the relevant Wikipedia article of each
Got inspired and found these, but having one single map with everything would be great indeed!
Good research. I will definitely put these in my research list. Something that also comes up a lot is https://castlesy.com/ but apparently is just for USA castles. I'll save that for the weekends.
I just found this too: https://www.castles.nl/ It has interactive maps, but some are very sparse (Germany's count is laughable).