tl;dr: toggle the physical Silent Mode switch on the left side of your iPhone on, then off again. Game audio should work properly after that.
There appears to be a bug in iOS 26 that can affect users with physical Silent Mode switches, like your iPhone 14 Pro Max. The fix is straightforward, and worked for a friend who encountered this problem: toggle the Silent Mode switch on, then off again.
Notably:
- The Silent Mode switch was off, and had not been turned on anytime recently, either before or after the update to IOS 26.
- Other system sound such as ringtones, videos, and so forth worked fine; only game audio was affected
- A reboot does not fix the problem.