I have a 23 Lexus RX350 with the same engine, bought new. I changed the original oil at 1,000 miles using M1 0W-20 and changed it again at 5,000 miles with PUP 5W-30. I am not concerned about a warrantee issue using a heavier weight oil for a few reasons, the main one being is that heavier weight oils are allowed for this same vehicle in other countries. This information is easy to find- check out the Australian Owners Manual. This engine has a timing chain and a turbo which I feel benefit from an oil with a higher HTHS than a 0W-20 oil provides. Plus, I push the engine hard and definitely fall within the "severe duty" category.
Personally, I plan on sticking to no more than 5,000 mile oci's and will stick to a 5W-30. Even in the colder climate that I live in, I had no starting issues last winter using this weigh.
Here is some information on the engine that you might find interesting:
https://www.toyota-club.net/files/faq/21-09-20_faq_t24-engine_en.htm.