iOS 11.4.1 it can still be installed on iPhone and iPad if you are interested in downgrading from iOS 12, or iOS 12.0.1, but the process is one of "luck" and not something 100% certain. Specifically, it seems that Apple would still randomly allow the installation of iOS 11.4.1 on iPhone, iPad, and iPod Touch these days, and the image below should confirm this.
iOS 11.4.1 requires a little patience and a few attempts before getting a confirmation that the installation is possible, so if you are very determined to downgrade, you must be very persistent. The installation of iOS 11.4.1 has been blocked by Apple since last week for iPhone and iPad, so normally it should not be possible.
iOS 11.4.1 Still Can be Installed on iPhone and iPad
iOS 11.4.1 is the last public version of the iOS 11 operating system that Apple released for iPhone, iPad, and iPod Touch, but there is no jailbreak solution for it. However, one will most likely be released before an iOS 12 fix appears for iDevices, so you can downgrade while you still have the chance to do so.
iOS 11.4.1 will not allow you to use a backup already made in iOS 12, so it is possible to lose some data if you decide to downgrade to this version of the operating system. Having said that, in theory, you should be able to install iOS 11.4.1 if you really want to, but you should also know what data you lose.
