Check out my lengthy descritpion of how I got my Govee Table Lamp 2 to connect at this link:
[Govee Table Lamp 2 - Matter Connection to SmartThings]
It may not be any use, but one thing that seems to be important, connect to ST as the first step. In my case, I did Govee app first, but then had to go back do a device reset to the Govee Lamp, go through Matter connection process and then finally reestablish the Govee App connection. The good news is that once the App has connected (the first time), it immediately reconnects any time thereafter without the need to do the whole pairing process again. It must keep the handshake parameters stored in the app so it works every subsequent time.
One final note, when you do a device reset, even though there’s no visual indication, the device is in “pairing mode” for ST for only 15 mins. If you don’t get the connection in that time frame, you have to reset it again. In my instance, upon reset, the instant I opened the ST app, it presented the Govee Lamp ready for connecting to ST via Matter and I followed the process via scanning the QR code, selecting my appropriate Wifi network and it connected.
Good luck!
JR