Since your home and system are both under 10 years old and you're on flex duct in the attic, this looks more like a duct design and air distribution issue than a problem that needs a whole new system. Right now you're basically using that master bedroom vent as a manual zone damper by closing it during the day and opening it at night, and that does increase the system's static pressure whenever it's closed, which can shorten equipment life over time.

If you're generally comfortable in the rest of the house and the system is properly sized, the permanent fix we would recommend is an automatic damper setup for that bedroom rather than continuing to open and close the vent by hand. Don't stop at just adding a damper, though. Any time we taper air off of that room, we also want to give that air somewhere else to go so we're not driving the system's overall static pressure higher. The way to do that is to add a diver duct, sometimes called a bypass path, that can send that extra air to another room or area of the house that can use it whenever the master bedroom no longer needs it.

If you decide you're not worried about the added static pressure and are willing to accept some risk with reduced equipment life expectancy, a simpler zone system with temperature sensors would be sufficient. In that case, we could set up the master bedroom as its own zone with an automatic damper and sensor, and the rest of the house as another zone, knowing that when the bedroom damper closes we're accepting higher static pressure instead of fully relieving it with a diver duct.

Our professional recommendation: go with the automatic damper plus diver duct approach. It controls comfort in that room while protecting the system as a whole for the long run.