Instead of changing the firmware, you can "work" around Apple’s App Store by sideloading modified apps (IPAs) like YouTube Reborn or specialized emulators.
99% of "modified IPSW" files found online claiming to "work" for iCloud removal are malware designed to steal data from your computer. How to Safely "Modify" Your iPhone 11 Experience
Modified firmware can contain keyloggers that record your passwords and banking info. Final Verdict