Start with an immutable source
Keep every original Takeout ZIP. Select all numbered parts as one job, inspect the preflight result and write repairs to a separate output folder.
A guide can help you understand the export, but the original archive is what lets you repeat the work when a tool, destination or matching rule improves.
Verify before importing
Compare counts, inspect failed and unmatched files, and test representative dates, locations, videos and dynamic photos in the destination application.
Do not delete the source because the first timeline looks correct. Keep at least one independent backup of both the original export and the verified output.