you shouldn't need two installs to tranfer.
Except for the part where you need the M$ store version installed to transfer your account... Unless the transfer takes less than 15 minutes that's not a good option
@Aida-Enna How exactly is it going to work?
You will, once you link Steam to Tweaker (more will be explained on Steam release once I do some quick final testing), be able to "hotswap" between launching the MS Store version and the Steam version in seconds using one singular install. So, once this is complete, you just change to the MS store version, launch it and get your code, close it and swap to the Steam version, launch it and put in your code.