Lightroom creates a folder to store previews next to each catalog. This folder is named
<CATALOG> Previews.lrdata so when a new version of Lightoom Classic is installed and migrates the catalog, it generates previews again for all the same images. This folder takes much more space than the new catalog.
Can the preview folder be shared between version of Lightroom? A link would be required to make it accessible via the names of the original and migrated catalog.
The Lightroom Classic Catalog FAQ mentions that certain catalog versions are compatible but I could not find anywhere that has a similar table for previews. Could they be all incompatible?