Hey,
Please take another look at our forum post which covers this, specifically the first FAQ.
Please Note: MetaHumans created in UE4.27 cannot be upgraded or migrated.
4.27 MetaHumans have never been able to be upgraded to 5.x. Outside of the one time operation to duplicate 4.27 MetaHumans into 5.0 that was completed when MetaHuman 1.0.0 was released.
Also take another read of the timeline, MetaHumans will continue to be able to be exported until the final stage of the shutdown.