Zuma overheating

[Just B]

First time here, kind of up a creek and would greatly appreciate any help. I have a 2018 Zuma 50 that I bought new 2 years ago from a Yamaha dealer. About a month ago the temperature light started coming on after about 2 miles or 5 minutes of around town riding at 25-30mph, which was really limiting where I can ride to obviously. I know that heat can really kill an engine and so far I’m pulling onto my street when the light comes so it’s only on for seconds but it’s every damn time, and now I've stopped completely to be safe. Here’s what I’ve done so far:

Replaced the air filter
Added just a little coolant to the overflow tank (wasn’t below the low mark to begin with)
Replaced the coolant (old coolant was clean and looked just fine)
Idled the engine with the rad cap off and burped some air bubbles out until the engine got hot then turned it off. Did this 3 separate times and by the third time there were no more bubbles.

None of that worked and I’m too far from the dealer to ride it there, plus I’d rather do it myself anyway. Some more info now – once the engine light comes on both the rad and the cap are cool to the touch, but the thermostat cover is very hot. So based on that and what I’ve read online I’m wondering is my thermostat stuck closed? I know I can get a new thermostat online and I think I’m handy enough to swap it out, but I know it could probably be other things instead or maybe in addition. If anyone has any guidance I'd love to hear it. Thanks.