Sorry, are you suggesting installing 21.02.x on my WRT3200ACM? Or trying a new router entirely?
My understanding from some posts here is that the 21.02.x release, and in fact any release newer than 19.07, results in an inconsistently unstable WRT3200ACM router. I would rather have a stable router and no Mysa thermostats, than a flakey router. For example, "Wireless is unstable on OpenWrt 21.02.0-rc3. Wi-Fi client does not disconnect but it won't receive/transmit any data for a minute or so. This happens regularly. I had no issues with OpenWrt 19.07.7" from this old thread. And there are some intermittent issues here about web interface stopping responding after some time, WPA3 networks stopping (I don't even know what that is, but it sounds not fun), "can't create an unencrypted guest network on radio1", "Two out of three Android OnePlus phones cannot keep connection to the 5GHz network anymore".
So I dunno. I worry if I upgrade the old WRT3200 to the latest firmware just to try and hack holes into the VPN and Firewall for my stupid Mysa thermostats, they will continue not to work AND in addition, a lot of other stuff also won't work.