New server startup parameters can break older mongoDB versions.  For example, loadBalancerPort (SERVER-60679) was backported to 5.0 and 5.2. So it's only applicable to 5.0/5.2/6.0+. MongoDb fails to start if we use it on 5.1. 

Cloud backup/restore can run into this type of mongoDb startup failures due to incompatible parameters, especially with rapid release versions. For instance, to restore a mongoDB version 5.1 snapshot to a version 6.3 target cluster, as suggested by the server teams, we'd need to start mongoDB 5.1 on the snapshot and successively upgrade it 5.1->5.2->5.3->6.0->..->6.3. We currently use the startup parameters from the target cluster to start all the versions in the upgrade path. Using loadBalancerPort as an example, since it doesn't work with version 5.1, restore will fail. 

It'd be hard for backup team to keep track of versions and incompatible parameters. Therefore, we'd like to request a new startup parameter to let server ignore unsupported startup parameters. We can apply this new parameter to its supported versions only.