In case someone still has issues with unconstraint virtual and ik bones in Unreal Engine 5.
Here are two ways how I work around them.
A custom IK Rig based solver to constraint virtual and ik bones directly during the IK Retargeting process.
Or constraint those bones with a Blutility.
In case you want to play around with the tools feel free to check out the open source UE5 plugin TTToolbox v0.3.