It’s doable, but as you noted, not with the official features. Also, the custom smart apps that you looked at require that the door Identify itself in a specific way, which apparently it is not doing.
(Just guessing here, but at the time that those were written, the only available compatible garage door opener‘s were two zwave devices, one to open the door and one as a Tilt Sensor. There was special logic required to work with the two in combination. However, most Wi-Fi controlled garage door openers do not treat the tilt sensor as a separate device, so that might be why it’s not working.)
However, even if it is seen as just one device, there are definitely ways that it can be done. 
Some use third-party paid apps, some are free but may have a more challenging set up.
Anyway, see the community FAQ for details:
FAQ: Get a Notification if Something is Left On, Open, or Unlocked for X Minutes (2020)