I installed macOS 27 on my spare machine, an old Mac Mini M1, and tested most of my apps. All of them seemed to work correctly except for a few minor issues. I'm actually optimistic about upgrading because of some of the performance improvements over macOS 26 Tahoe.
The biggest issue that I noticed was that the app compression feature in Revok does not seem to compress anything, though it does correctly read the compression state. I disabled that feature on macOS 27 as it could be due to a regression in some API function it relies on. I'll wait to macOS 27.1 to upgrade my main Mac and work on a longer-term solution and do more thorough testing on my other apps. I'll likely make macOS 15 the minimum version I support, which gives my apps 3 years of macOS compatibility. Apple is making it harder and harder to support older versions.