I have Music Maker 2020 at the moment, I am planning on buying the 2021 version in the performer edition package, but want to put it on a new PC that i have just bought.. Will I be able to transfer my soundpools and instruments over to the new version on my new PC...?
Your Soundpools and instruments are bound to your user account. If you use the same user account for Music Maker 2021 you can just redownload everything you currently own on your new computer.
In case of your Soundpools you can also copy the folders over to your new computer if you don't want to redownload them to save bandwidth and time. But this will not work for the instruments. They will need a new download.
i would also download the soundpools from the Music Maker Store on the new computer. That way you always have the latest version of the soundpool and there are no copying errors.