The LINQ expression could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation

The issue is that you are trying to do a string.Contains within an Any expression which EF will choke on trying to compose down to SQL. Cleptus is on the nose, to build a predicate for the Where clause OR-ing the term comparisons. Otherwise your code should work without the contains check, but rather an equality check:

Without Contains: (equality check rather than LIKE %name%)

var terms = title.Split(' ').ToList();
items = items.Where(w => terms.Contains(w.ItemName)); // IN clause.

Built expression:

var terms = title.Split(' ').ToList();
Expression<Func<Item, bool>> predicate = (Item) => false;
foreach(var term in terms)
    predicate = predicate.Or(x => x.ItemName.Contains(term));

items = items.Where(predicate);

So for each term in the title, we OR a match using a LIKE %term% on the ItemName.