For "most compatibility", it has always been necessary to not keep up. It's common practice to target the oldest version of MacOS that your app is capable of supporting (and that you're willing to test). You do that by leaving the build machine on the appropriate version of MacOS/XCode.
In other words, if AxeEdit doesn't need new features that have been introduced to MacOS since 10.13, then there's no need to upgrade the build machine past Sonoma and XCode 15. That will provide support for MacOS 10.13 for years to come. I'm pretty sure FAS understands this. For example, AxeEdit had a minimum of 10.7 for years and that only recently changed to 10.13.