The release candidate builds save their profiles to the same directory as the last release, however if you already tested any of the PrusaSlicer 2.4.0 alpha or beta builds, you will be offered to import the recent alpha or beta profiles. For new features in the 2.4.0 series, please read the release logs of the 2.4.0 alphas and betas. This release candidate fixes bugs found in the first release candidate.