I rummaged through Minecraft Support and the migrate to microsoft account thing said here
If you migrate your Mojang account to a Microsoft account that has been used to play Bedrock (on any platform), then yes - you'll be able to access both games with that account.
Does that mean that if everyone has a Microsoft account and Minecraft Java, that you can get the Windows 10 Edition for free?
No, that doesn't mean that.
A few years ago it was a short one.
You needed minecraft Java then you could download bedrock for free, but that doesn't work anymore