I was also having this issue. I hate how complicated they (M$) made things.
In my case, I logged into minecraft.net and installed the minecraft launcher.
When I launched the game, I got the same error message you got, same welcome screen after starting the Minecraft Launcher.
What worked for me, and seems to from others responses is to close the Minecraft Launcher. Then try searching for the Minecraft Launcher in the Microsoft Store (even if its already installed, like yours and mine were, search for it again). Then, while you are in the Store, and you see the Minecraft Launcher app, there *should* be a blue "Play" and a grey "Get" button somewhere to the bottom right of the image of the Minecraft dirt block. Click on the grey "Get" button. (You should still be in the Microsoft Store, not having launched the Minecraft Launcher)
Even though I had migrated my account and installed the launcher, I still got the same error message until I clicked the grey "Get" button inside the Microsoft store. Once I did that, I guess it associated the Minecraft Launcher with my account. I was then able to play by clicking on the blue "Play" button.
I hope this helps you.
Thanks! This fixed the launcher for me. Gonna be honest, this was mildly upsetting to deal with. I installed Minecraft initially just last year and all I had to do was download from Mojang and everything worked. Like seriously, why the hell do I need to go download the launcher from the Microsoft store when I already have the launcher from the main Minecraft website?