How many gigs in iOS 13 and related apps on a new iPhone11 Pro Max?

If you look in System, which is where the iOS is counted, that is going to give you the best idea. Your question was not as clear as to what it was you were looking for. I have and use an iPhone 11 Pro 64GB. I have several apps, photos, and music. I still have around 23GB of space left on it. I generally have more, but we have a new grandson, so I've been taking and saving a lot of photos since he was born in December 2019. I will clear my Recents photos soon after I move them to the computer. Been a little too busy to do that of late. Then I also go through and check on Messages for photos to keep and move them to the computer as well, then delete the messages. I've been able to get along with a 64GB model for several years now.

When I installed the iOS 13 update on my device with iTunes, it was about 4GB.

You're welcome.