ToList() or ToArray()?

Both ToList() and ToArray() force execution of a deferred LINQ query and pull the results into memory. The question isn't which one 'runs the query' — they both do. It's what you do with the result afterward.

Reach for ToList() when the collection grows or changes

var items = await _db.Products
    .Where(p => p.IsActive)
    .ToListAsync();

items.Add(newProduct);   // List<T> supports add/remove
items.RemoveAt(0);

List<T> is the right default for most application code: it's flexible, supports Add/Remove, and is what most APIs expect. In EF Core, ToListAsync() is the idiomatic materialization call.

Reach for ToArray() for fixed, read-only sets

var ids = await _db.Orders
    .Select(o => o.Id)
    .ToArrayAsync();
// Fixed size, read-only iteration, minimal overhead

The difference is rarely a performance bottleneck on its own — the real cost is materializing more rows than you need. Project with Select, filter in the database, and only then decide on List vs Array. Shape the query first; pick the container second.