Das kennt ihr:
For those interested in fixing this problem by themselves, the solution is quite simple really, although people prone to clumsy errors should probably refrain from trying this, as failure to follow the instructions to the letter might cripple your Mac.
First of all, you should be certain that you have an up-to-date backup of your High Sierra disk and that you know how to use it in case something goes wrong. If you don't know how to restore from a backup, don't read any further.
Secondly, you should disable SIP, at least for the time being. Boot your Mac from the High Sierra Recovery Partition. Once booted, go to the Tools menu and open Terminal. Then, in Terminal, enter
csrutil disable
Reboot your Mac normally.
Next you need to find out your computer board id. It's different for every particular Mac model. For instance, my Mac board id is "Mac-F221BEC8" because it's a Mac Pro 5,1 of 2010. If it had been a Mac Pro 5,1 of 2012, its board id would be different. If you don't know yours, Google your specific model until you find two or three corroborating testimonies that what you find is, indeed, your computer board id.
So, repeating the explanation above that I posted 29 days ago, do the following:
Using TextEdit or a similar tool, open /System/Library/Frameworks/IOBluetooth.framework/Versions/A/Resources/SystemParameters.plist. You should see a list of board ids. Find the relevant entry for your model. Once found, you should see that it has one subelement called "ContinuitySupport". Presumably, it has the boolean value "false"; that should be changed to "true". Save the file.
Study this command (it's one single line):
sudo -E perl -pi -e "s/\Mac-00BE6ED71E35EB86/\Mac-F221BEC8\0\0\0\0\0\0\0\0/" /System/Library/Extensions/IO80211Family.kext/Contents/PlugIns/AirPortBrcm4360.kext/Contents/MacOS/AirPortBrcm4360
Notice that "F221BEC8\0\0\0\0\0\0\0\0" is the "short" board-id (excluding the "Mac-" part) of the Mac Pro 5,1 of 2010, followed by eight nulls, making up the 16 bytes used by the current "long" board ids. Now, edit the above line (for instance, using TextEdit) so that, instead of "F221BEC8\0\0\0\0\0\0\0\0" you paste whatever board id your computer has. If it is eight bytes long, remember to add the eight nulls. Now, double check that your modified line is the correct equivalent of the instruction above for your computer.
Open Terminal. Select your previously edited instruction of step 2 and drag it to your Terminal window. Press Enter. You'll be prompted to enter your administrative password. Do it.
Now you only need to delete the kext cache:
Enter this in Terminal:
cd /System/Library/Extensions/
sudo touch .
Boot your computer.
Instant Hotspot, Handoff, Universal Clipboard and Apple Watch Unlock should work. If they don't, your BT/Wi-Fi card might not be compatible with the hardware identified by the AirPortBrcm4360.kext. If there isn't a particular kext for your card, you may be out of luck.
Another explanation for the above procedure not to work might be that there's something wrong in your Apple ID data on your devices and/or in the relevant choices you make as to how Continuity/Handoff should work.
Lastly, chances are you might have done something wrong in following the above procedure. Repeat it slowly, just in case.