I can no longer select up to five tiles on my mobile game - has this feature been discontinued?
No, the feature still exists. Your digging queue is probably turned off, that happens sometimes. You can find this in your settings ⚙️. While you are there, make sure your gem confirmation is also turned on 🙂
You should periodically check out your game settings menu.
Especially after an update......always make sure that your "Gem Confirmation" is switched ON (green)