Can the .PAK files that I package in Unreal Engine 5.3 preview version be mounted by the client developed in Unreal Engine 5.3 release version?
anything created in the Preview version of the editor “SHOULD” be compatible with the that version of the engine when it fully releases.
be mindful of any feature labeled “experimental” as those could be withheld from the Stable version release (this “should” only happen if it is found to be inconsistent, or not behaving “as intended”)
also keep in mind that the previews are mostly there to “stress test” the features (mainly those marked experimental) to see if they are ready for the Stable release.