Migrating from Lightroom to Lightroom Classic

You need to understand that your existing "folder/subfolder" structure in Lightroom is not the same as a folder/subfolder structure in LrC. In Lightroom, it's a way of organising your existing albums into virtual containers and as such it would be the equivalent of a Collection Set hierarchy in LrC. It is unrelated to the physical storage of the images on local disk.

There is no easy way of migrating that virtual structure from Lightroom into a physical disk-based folder structure, you would be better advised to accept the dated folder structure and instead concentrate on syncing the existing album and folder structure into the equivalent Collection Set/Collection structure in LrC. The easiest way of doing that would be to enable syncing in a new empty LrC catalog (having first set the location for downloaded images and the optional date-based folder structure via the LrC Preferences>Lightroom Sync tab), which will then cause a copy of all the existing images in your cloud account to be downloaded into that new catalog, and placed into the equivalent collection/collection set organisation.