I understand your frustration with PUBG lag on iOS 14 and the impact it has on your gaming experience. It's important to note that app performance can be affected by a combination of factors, including the device's hardware capabilities, the app itself, and the iOS version. Developers continually work on optimizing their apps for the latest iOS updates, and sometimes issues can arise.
To address this problem, I recommend you contact PUBG Mobile's support team and report the issue. They can investigate the problem and work on potential fixes. Additionally, make sure your device has the latest software updates and consider closing background apps that might be consuming resources. You can also try lowering the in-game settings to reduce the strain on your device's hardware. Solution can also be find here: https://delhitrainingcourses.com/blog/pubg-mobile-high-ping-lag-problem-solution/
It's frustrating when updates cause issues, but providing feedback to the developers can help them identify and resolve these problems. iOS updates may also improve stability, so keeping your device up-to-date is beneficial.