Selecting Reimport on a DataTable created in editor no longer triggers selection popup.
"The change in behavior seems to be related to changes to UReimportDataTableFactory::CanReimport() which now returns (false) when there is no previously associated import file. This used to be handled by FReimportManager::ValidateAllSourceFileAndReimport() which allows CanReimport to either return an empty list of filenames or blank filenames."
Verified in MAIN at CL 4888291
4.20 Result: Windows explorer appears allowing you to specify a source CSV
4.21+ Result: No window popup
Workaround - Export data table as CSV and import this file to Content Browser.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-69679 in the post.