How do I get some kind of warning or indication before the screen locks in macOS?

In macOS I have fairly short times for auto-screen-lock (2-min on battery, 5-min on power), with immediate password requirement of course, for security. I usually lock manually, but these are there as a backup. However, because the lock is instant, it means there are occasions when it locks when I don't want it to. For example I'm reading code and thinking, or I stopped to look in a book then looking back to the screen. I'd like a warning before the screen locks, for example fade down to 50% then wait 5s before actually locking. I think it may already do this when on single-screen (laptop-only), but it doesn't happen when using external monitors. If I had such a feature: * My deep thought would never be interrupted by having to unlock. * I could set the auto-lock times both down to 1 minute (only reason I choose 2+5 is because it's a compromise to minimise unwanted locking, but it still sometimes happens). If anyone knows of a way to get such a warning/indication before screen-lock, please let me know.