And to reply myself: I found a solution. It is presented in my post under another topic .
I'll repeat it here for your convenience:
I have found a tested and working solution for those, who cannot remove XFENCE.kext from /Library/StagedExtensions/Library/Extensions/ - even via Single User mode:
Delete the actual kext from /Library/Extensions/ first, then run "KextWizard" (downloadable at https://mac.softpedia.com/get/Utilities/Kext-Wizard.shtml) and enable both checkmarks under "System/Library/Extension, i.e. "Repair permission" and Rebuild cache" - then click "Execute".
This removes the stubborn XFENCE.kext from the cache (that /Library/StagedExtensions/Library/Extensions/ actually is) and keeps it from being activated over and over again.
I strongly believe that XFence is dead as Mr. Zdziarski is now working at Apple and regardless of the fact that F-Secure bought it from him to gain access to its technologies to be able to implement them into their endpoint sec. products, Apple is "replacing" XFence's features balanced with usability (and of course, because of that with significant limitations) built into the latest v. of macOS.
This topic has been closed due to inactivity. If you would like to discuss this topic further, please start a new post.
You can reference this topic in your post by adding this link:
Visit the Community
Check our Forums or How-to & FAQs for advice or answers
View User Guides
Refer to our getting started guides and product manuals
Talk to our Support and get answers to your questions