Unable to downgrade from iOS 26 to iOS 18 on iPhone 15 Pro Max

I have tried to get rid of iOS 26 and I thought I was back on iOS 18 but when I was logging in they asked me to download iOS 26 again it took me five days to try and get rid of iOS 26 and now I thought I went back to iOS 18 and now I’m stuck on iOS 26. I’ve had so many issues with iOS 26 it’s made my phone really warm and the battery health goes down a lot more. Have the iPhone 15pro max and I have used iOS 26 for last God knows how many days it’s something I don’t enjoy something I probably won’t be getting used to but I did some research and it said Apple won’t force you to get iOS 26 and then after resetting it and I thought I was on iOS 18 Apple is making me download iOS 26 on my iPhone 15 Pro Max

[Re-Titled by Moderator]

Original Title: iOS