I have a 500Mb NVMe C drive that is almost full with MSFS 2020, and a SSD drive D that is mostly empty. Its main use is to store the scenery cache at the moment. My Steam edition of MSFS 2020 is on my C drive.

Can/will MSFS 2024 load straight over the top of 2020 and replace it, integrating all the add on planes, OR, does the install need a clean drive to load and just copy the Community folder across?

PS I've just found out that a capital C or D plus a colon : . produces a "smiley", hence the lack of " : " above in the drive descriptions. 😄  😧 

14 minutes ago, thecanarian said:

Can/will MSFS 2024 load straight over the top of 2020 and replace it, integrating all the add on planes, OR, does the install need a clean drive to load and just copy the Community folder across?

My understanding is that MSFS 2024 will install as a separate app, not sharing anything with MSFS 2020.

You can then carefully copy any Community folder content from the 2020 app to the 2024 app.

I expect to run the two sims side by side for a while, until I decide that MSFS 2020 has no use anymore.

In your case, I would suggest installing MSFS 2024 onto your drive D... that is the approach I am taking.