If you are looking to downgrade your iOS then it is not possible by default. Apple does not allow users to downgrade to the previous version of their software once they have upgraded to the latest version but you can un-officially downgrade to previous versions by using jail break.
If you are going to downgrade then you must first check the compatibility of the device with the iOS version that you want to install or downgrade. Downgrading to a previous version of iOS is not an idea that sits well with many iPhone users as it has several security issues as well as requires unofficial and unsafe ways. But you can downgrade by doing the following process.
Looking back to the start when apple launched its first device and software, we can sense that Apple has come a long way towards innovating their technology. Apple upgraded their operating systems since its first launch. They enhance and reinvented their operating systems every year to redefine their technology and features on their devices.
iOS is the Apple operating system that Apple’s iPhone is using since their reveal. Over 13 years, Apple has frequently added solutions to security issues and made the App store more prolific along with more Apple apps like Apple Music, Podcasts, etc. The most recent version of iOS is 14 that Apple introduced in its latest iPhone 12.
One of the many iOS versions, one that Apple introduced back in 2017 was iOS 11.1.2 to cover the bugs because of which iPhone X screen became unresponsive due to temperature drop. iOS was released to fix these iPhone X issues. iOS 11 is compatible with iPhone devices ranging from 5S to iPhone X, iPads and iPods, etc.
As all of us know that Apple software restricts users to installs applications or other software applications that are not authorized by Apple's app stores. The technique called jailbreaking was introduced in Apple's iOS by which the user can remove software restrictions.
Although jailbreaking bypasses the restrictions of the operating systems and allows you to install unauthorized apps on your Apple device, Apple won't be responsible for the security risk it might take for your device and considers it a violation of its warranty.
Now, if your iOS 11.1.2 compatible device upgrades to the updated version of iOS, then how are we going to use the jailbreaking feature to enjoy the more features in iPhone than how to downgrade to IOS 11.1.2, is what we are going to discuss.
Many tools for jailbreaking an iPhone are available, but still, some operating systems don't support jailbreaking at all. If you are using recent models of iPhone with the latest iOS version then it is most likely that your device will not support jailbreaking, you will have to use some tools or just downgrade your software to the previous operating system.
If you are looking forward to upgrading or downgrading to your desiring iOS, then it is probably better to do it within the time frame of available update. Apple is pushing updates at a rapid pace so it is better to utilize the updates at a convenient time. So, to downgrade to iOS 11.1.2 follow these steps.
If you are planning to keep your previous data, then you will have to create a backup of your device. I recommend you to create the backup on the personal cloud rather than iCloud as it will take less time and can update from every version of iOS 9/10 to iOS 11.1.2 and restore from your backup.
This case will not work if you are on the firmware iOS 11.2. So, if you try to completely restore your device down to iOS 11.1.2 and then try to restore from iOS 11.2 backup, iTunes will not allow this as the backup created on the IOS 11.2 is new for the iOS 11.1.2. So, if you want to save your data coming from iOS 11.2 down to iOS 11.1.2, then you will have to choose a slightly different path for the restoration process.
The other method that we can use for the same purpose is:
The modification for doing so is to select the alt or shift button on the windows. Click the check for update button which will put up the dialogue box in which you can select the iOS 11.1.2 IPSW, then it will downgrade to iOS 11.2 and will keep all your data instead of restoring completely. That is how your device downgrades to iOS 11.1.2 from any other operating system.