I guess it is the
reagentc /setreimage /path ...we need to use for this after assigning a drive letter to the volume on the recovery partition. Why Microsoft did not use this technique to apply the update initially nor suggested this as a workaround?
It's only this:
reagentc /disable
reagentc /enable
with the new recovery partition in place. The Windows RE addresses the recovery partition automatically.
But it can't be the official solution as it requires BitLocker disabled.