Now we can change iOS11 resolution without that annoying glitches. But for your information, this tutorial is not very stable. 

Operations

Step 1 In Filza, navigate to /var/mobile/Library/Preferences and find out the file ‘com.apple.iokit.IOMobileGraphicsFamily.plist’

Step 2 Change your resolution in this plist, then save it.

Step 3 OpenTerminal app or use CocoaTop for below steps.

Step 4 Kill cfprefsd and backboardd

• To do this in Terminal,

type these commands as root,

1st: killall cfprefsd 2nd: killall backboardd

Finally, it’ll restart SpringBoard.

You need to repeat these steps if you restart and rejailbreak your device. But before doing above steps, make sure to set your default resolution and respring first. ie., your device must be in default resolution before doing above steps.

iPhone resolutions:

• iPhone 5s / iPhone SE: 1136x640 

• iPhone 6 / iPhone 6s / iPhone 7 / iPhone 8: 1334x750 

• iPhone 6 Plus/ 6s Plus / 7 Plus / 8 Plus: 1920x1080 X: 2436x1125

Source: reddit