I’m on windows 10, and I followed every instruction from How to compile Aseprite 2020 || Get Aseprite for FREE! - YouTube, and that was the error message I got when I ran C:\aseprite\build>ninja aseprite
Every forum thread I found with people having this problem either their was no answer or the answer was very unclear or for another operating system.
this video helped
https://youtu.be/21-xiWaIV9I?si=jutAJY0kS-HX-QiW