#34344 will allow users to configure whether parameterized collections should parameterized by default (e.g. via OPENJSON, this is the current default), or constantized (as Contains did before 8.0); we are also considering changing the default mode back to constantization in 10.
If users choose to default to constantization, there should be a way to specify for specific collections of specific queries that they should be constantized. EF.Parameter was already introduced in 8.0 (#28151) as a way to force parameterization even when the query contains a constant; this can be useful for some scenarios of dynamic query tree construction, as well as F# where captured variables are always constantized.
We should make EF.Parameter also cause the parameterization of collection parameters, similar to how EF.Constant can cause them to get constantized.