Hello and welcome to Apple Support Communities, Bert!
I understand you're trying to get screen sharing to work with your Mac mini, since now it only works while in safe mode. I'd be happy to provide any information that may help.
Let's start with this article: macOS Sierra: Set up and use screen sharing
It's a good idea to start the setup process again, even if you've already set it up previously.
Then, move on to this article: macOS Sierra: Share your screen using Back to My Mac
If you have an iCloud account, and you have several computers connected to the Internet, you can share the screen of one computer with other computers.
For example, if you have a Mac at home that’s connected to the Internet, you can share its screen with a Mac you use at work. You can control that Mac, move files and folders, open or close apps, and even restart it.
Follow these steps for each computer whose screen you want to share.
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Choose Apple menu > System Preferences, then click Sharing.
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Select Screen Sharing or Remote Management.
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Next to “Allow access for,” select “All users” or “Only these users.” If you permit only listed users to have access to the screen, click the Add button 
and the Remove button 
to edit the list.
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Choose View > iCloud to open iCloud preferences.
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If you aren’t already signed in to iCloud, enter the Apple ID you use with iCloud, then click Sign In.
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In the list of iCloud features that appears on the right after you’re signed in, select Back to My Mac.
If you're still running into issues after trying these steps, answer the following:
1. Does this happen within another user? You can use these steps to test that out:
How to test an issue in another user account on your Mac
2. Did you setup your Mac from a backup after installing the new hardware?
Thank you for using Apple Support Communities.
Have a great week ahead!
