I got my betta on September 1, 2021 so I've had him for 7 months. We just returned from a unplanned 3 week trip and he's doing fine. Between my automatic feeder and my daughter checking on him mid-way through, we got him through. I cleaned the tank before we left and brought the water level up to touching the underside of the white top. When we returned, it was about 2 inches down, so I added RO purified water then did a 10% tank change. I'll do another change tomorrow.
Overall, the tank is the bare minimum size for a betta. I think he gets bored, but he perks up when he's hungry. When he dies, I will probably get a freshwater shrimp or a snail.