Calendar synchronisation between iMac and iPhone does not work anymore since update

Incase the user may have over looked aspects of the information in previous Link

Below is a Copy and Paste

Sync content between your Mac and iPhone, iPad, or iPod touch

You can select the information you want to sync between your Mac and device. You can sync all items of a specific type (for example, all your movies or photos). Or you can select specific items (for example, some of your movies and some of your books), which gives you more control.

After you select the content you want to sync, the items are updated whenever you sync your device and your Mac.

The first time you set up syncing, you must connect your device to your Mac using a USB or USB-C cable. After you connect the device, the device icon appears in the Finder sidebar and selecting the icon displays syncing options. You then select which items to sync.

If you have an iPhone (with iOS 5 or later) or iPad, you can also set up to sync wirelessly when your Mac and device are connected to the same Wi-Fi network. See Sync content between your Mac and iPhone, iPad, or iPod touch over Wi-Fi.

For more information about syncing, see Intro to syncing your Mac and your devices.

Sync all items of a content type

1. Connect your device to your Mac.
2. You can connect your device using a USB or USB-C cable or using a Wi-Fi connection. See Sync content between your Mac and iPhone, iPad, or iPod touch over Wi-Fi.
3. In the Finder  on your Mac, select the device in the Finder sidebar.
4. 
5. If you connect your device to your Mac using a USB cable and don’t see the device in the Finder sidebar, see If your device doesn’t appear in the sidebar. 
6. Click the type of content you want to sync in the button bar.
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8. Note: If you use iCloud Photos and Apple Music, your photos and music are synced automatically using iCloud. When you click Music or Photos, no options appear for syncing.
9. Select the “Sync [content type] onto [device name]” checkbox to turn on syncing for that type of item. For example, select the “Sync movies onto [device name]” checkbox to sync your movies.
10. 
11. With the checkbox selected, syncing is set to transfer all items of that type to your device. 
12. Repeat steps 3 and 4 for each type of content you want to sync.
13. The bar at the bottom of the window shows how much free space remains on your device after you sync. Move the pointer over the bar to view details about the content you’re syncing.
14. When you’re ready to sync, click Apply.

You can choose to sync your Mac and your device automatically whenever you connect them. See Turn automatic syncing on or off.

WARNING: If you delete an automatically synced item from your Mac, the deleted item is removed from your device the next time you sync.

If you want to sync individual items instead of all items of a content type, see the following: 

• Sync music to a device
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• Sync movies to a device
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• Sync TV shows to a device
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• Sync podcasts to a device
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• Sync audiobooks to a device
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• Sync books to a device
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• Sync photos to a device
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• Sync files to a device
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• Sync contacts and calendars to a device

Before disconnecting your device from your Mac, click the Eject button  in the Finder sidebar.

When the User says " the direct calendar synchronization between mac and phone (not using icloud) does not work anymore. "

Does the user mean by Cabling the iPhone Directly to Computer or something else

Link below for a Physical Connection to computer using Finder

Sync content between your Mac and iPhone, iPad, or iPod touch - Apple Support (CA)

Then have a few suggestions ;

1 - Get Support Choose a product and we’ll find you the best solution.Start now and open an Apple Support Ticket as they are Apple Employees to deal will these types of issues . 

2 - Product Feedback - Apple and make it known to Apple regarding this ongoing issue 

Ok and congratulations on using the iPhone for that may years

So, is the User ( you ) saying the instruction from suppled link above;

1 - does work as intended

2 - does not work as intended

3 - has not yet tried using the Finder

I have also had similar issues with syncing my calendars, often seemingly random if items are transferred from my iPhone to computer (not related to newest, literally seems random although there must be something Apple messed up). Currently my calendar does not update on my Macbook from my iPhone with latest iOS. Hopefully this can get fixed. It would also be nice if one could choose to replace the computer calendar with the one from my phone, since that is what I have on me when new items come up for my schedule.

[Edited by Moderator] 

I did, unfortunately they are baffled as well (escalated to senior tech support level). If I get a solution, I will post it.