I did that once. No, you don’t need to reinstall the whole Sims.
The idea is to copy yourself the most biggest directories “Official” and “Community”, where they should land on your new drive.
For me those folders are currently under "f:\Games\MSFS2020", and the main game directory (with the .exe) is in “F:\Games\SteamLibrary\steamapps\common\MicrosoftFlightSimulator”
After that you uninstall the Sim through Steam, and you reinstall it. When MSFS ask for the target directory, provide the new path on your new drive where “Community” and “Official” are. It will find than the 2 big folders are already their, will not download them, and will only install the main directory.
I hope I’m clear…