I, on my W11 computer, also initially had some issues running JTool (the editor that KeyTool is a mod of), but I managed to fix them through downloading the Microsoft Visual C++ 2010 x86 Redistributable - 10.0.30319 package. I don't remember having to do anything else to get JTool to work, so give downloading that package a try and let me know if it works.
I downloaded that but it didn't work for me. Also, now that I look at it again, my error is slightly different:
___________________________________________ ############################################################################################ FATAL ERROR in action number 1 of Create Event for object oWorld: global variable name 'savePlayerXScale' index (100069) not set before reading it. at gml_Script_loadPlayer ############################################################################################ -------------------------------------------------------------------------------------------- stack frame is gml_Script_loadPlayer (line -1) gml_Script_loadMap gml_Script_loadStartupMap gml_Script_mainInit gml_Object_oWorld_Create_0
Press Alt+Click on a key, door, or other object to open up a code editor. You have to set their variables with code to make them function properly, even single keys/doors, or else they break in the editor. How it typically works is you set variables with code formatted like "variable=value;", with the semicolon at the end of every line of code. The most common variables are "count" for key/door count, "w/h" for door width/height, "c" for door lock color, "cs" for door base color, and "type" for key/door type. You can read more about them in the instructions file attached.
Key counters work a special way. Basically, the counter itself is the "list" of key counts to show, and you add the different key colors to that list, which it then auto-generates the counter graphic with. The basic code looks like such "s0=COLOR;s1=COLOR;s2=COLOR;" etc, with each "s" being the first, second, third row of the list (starting from 0), and "COLOR" being replaced with a number which correlates to the key color, which you can find in one of the readme files. You can also set "long=(Either 0, 1, or 2);" to make the counter longer.