macOS’s Gatekeeper blocking an older, uncertified app. Fix: Open Terminal and type: sudo spctl --master-disable Then try opening the app again. Alternatively, right-click the app and select Open (not double-click).
Consider using P-touch Editor 6 (free, from Brother) or P-touch Editor 5.4 (if available for your older macOS). Version 5.1 was primarily for Windows XP/Vista/7 and very old Mac OS X versions (10.5–10.9). p touch editor 51 download mac top