Landing page tests were deprecated on May 1, 2019. You are no longer able to create new tests in Search Ads 360, and any previously running tests have stopped running.
In any Search Ads 360 account, you can use ad copy tests to create duplicate ads with different landing pages. For a complete explanation of the alternatives to landing page tests that Google Ads provides in addition to ad copy tests, see test landing pages.
Historical metrics on your landing page tests will continue to be available in the Landing page tests tab in the left navigation panel. Learn more about reporting on landing page tests.