If the above solutions are useless for you, it is strongly recommended that you can take advantage of iOS system recovery software - Joyoshare UltFix to fix iPhone screenshot not working. As one of the most excellent and popular iOS system issues repair tools, Joyoshare UltFix is designed to repair over 30 kinds of iOS system problems quickly with no data loss.
Offered "Standard Mode", you will fix many common iOS system issues including iPhone vibration not working, iPad Home button not working and so on without losing data. Besides, you also can restore your iPhone to factory settings with "Advanced Mode" if you need. Importantly, it offers free one-click enter/exit recovery mode function. By the way, it supports the iOS version 12.3. With these features above, it must fix screenshot not working iPhone issue successfully.
Key Features of Joyoshare UltFix iOS System Recovery:
Repair iPhone screenshot problem without data loss
Provide two repair modes for you all
With one-click enter/exit recovery mode function
Compatible with all iOS devices