The red dots are TextureRects in the map.scn file. The tooltip text and which points connect are stored in explorationregions.gd. map.gd uses those2 files to determine where to draw the lines when you hover over a red dot.
.scn files are not text files and are best edited using the Godot Engine. A new project can be created and Strive can be copied into the project folder to allow basic access. Beyond that it gets rather complex.
Alternatively, once map.scn has been loaded by the game, any script file can be used to create new red dots by duplicating an existing TextureRect.
explorationregions.gd should be fairly straight forward as it is a simple text file . I'd recommend starting from a copy an existing region.