So to answer what should have been the question:
I want to list methods defined through a list of strings (defining full names), that are obsolete + for each method matched, list the obsolete types/methods/fields used
let methods= Application.Methods.WithFullNameIn(
"Namespace1.Class1.Method1()",
"Namespace2.Class2.Method2()") // Put more full names here
.Where( m => m.IsObsolete)
from m in methods
// Here we cannot easily define m.TypesUsed, hence we use an astute
let obsoleteTypesUsed = m.ParentType.TypesUsed.Where(t => t.IsObsolete).Where(t => t.IsUsedBy(m))
let obsoleteMethodsUsed = m.MethodsCalled.Where(m1 => m1.IsObsolete)
let obsoleteFielsUsed = m.FieldsUsed.Where(f => f.IsObsolete)
select new { m, obsoleteTypesUsed, obsoleteMethodsUsed, obsoleteFielsUsed }