Tahoe (26.6.2) here, with a single app ( @ttscoff’s FileRouter) set as the default application for both .txt and .md
Some side-effect of a growing inflexbility, or sandbox vigilance, on Apple’s part, about using different applications to work on the same file, or with the same file extension ?
Apple quarantine warning - Bike Outliner - Hog Bay Software Support
( The FileRouter solution to that is working well here. I haven’t tested it on macOS 27 )