Gambling losses are an itemized deduction, so, yes, they will not be counted if using the standard deduction on your return. Plus, gambling losses can only be deducted up to the amount of your winnings.
The standard deduction was increased significantly in 2018 as part of the tax reform changes from the Tax Cuts and Jobs Act of 2017. Therefore, even if your itemized deduction total (including gambling losses) does not exceed the standard, you still are getting a better tax situation by being able to take the larger standard deduction on your return.