UE5 has been out for two years and we still cannot export using its skeleton, anyone interested in this should vote for it here. (not my feedback post but it gets the job done) 
https://www.reallusion.com/FeedBackTracker/Issue/UE5-Skeleton-Export/1/Unreal%20Engine%205%20Skeleton

Waiting two years for a major thing like this is not really reasonable, Reallusion software is very expensive, I expect better support.