I started with Lightroom using the Cloud based version but now want to convert to the Classic Desktop version with Catalog setup. Do you know if I will then lose all the edits currently performed or is there a way of converting to the Desktop version and retaining prior work.
The simplest way is to create a new empty catalog in Classic and sync it with the Cloud, as that will download all images stored in the Cloud to your local hard drive. Before enabling syncing in Classic, first open the Classic Preferences>Lightroom Sync tab and use the options there to set your preferred location for storing of those downloaded images. Note that Classic can put the downloaded images into capture date-based subfolders beneath the top-level folder that you designate, you would enable that option and specify which date format you want to use on that same Preferences tab.
Once you have done that, click on the cloud icon, top right of the Classic window and click on Start Sync. Then wait....Classic will start downloading all the cloud-based images and add them to the catalog. All edits that you made in Lightroom will also be downloaded, and if you applied metadata in Lightroom you will get some of that, but not all. Specifically NOT sysnced are Keywords, location data (but if the images have GPS coordinates set then Classic will do reverse geo-tagging to suggest the appropriate location data), and facial recognition data.
Once all is downloaded and backed up you can then decide what you want to do with the images in the cloud.
An alternative, and much slower way, of migrating from Cloud to Classic would be to export all images from the cloud to your local hard drive using the "Original" option, then import them all into a new Classic catalog. That will preserve your edits AND it should preserve any keywords and location data that you applied in the Cloud.