Is a data export useful if another service cannot read it?

An export can help you inspect or retain records even when another service cannot import every field. Data portability is not the same as transferring every feature. Compare the export format with the receiving service's supported fields, and keep the original archive private while investigating.

That answers something I was unsure about: an archive can still be useful for reviewing my records even if it is not ready to import.

Would an example with made-up records help show which fields a receiving service might ignore?

I'd like a guide to distinguish reading an export from migrating an account. Those sound like different projects.