The approach I tried was a Rust/Tauri true lightweight overlay with context awareness, so that each note feels like an extension of the program you're using and automatically hides if you minimize/alt+tab to a different program. The active notes never lose focus so you can even position them as part of UI when gaming.
Let me know what you think! It's free to install and try but I'll be happy to send free premium keys to anyone willing to stress-test the app.