iMac Mojave & High Sierra cannot connect external monitor after update

Please forgive the long post, but alot of steps taken here.

I have an iMac 27" 2013 qaud core i7 (full specs attached below)

and I can no longer run external monitors since the update to High Sierra 10.13.6 or Mojave 10.14.2.

Previous versions of HS were working fine.

After I updated from HS 10.13.3 to HS 10.13.6 the external ASUS 23" monitor will no longer

connect, although it would detect a profile of the ASUS monitor in the display settings of the mac yet

nothing would actually display on the 2nd monitor.

External monitor is an ASUS VS247HR 1920 x 1080

Everything has been fine up until that update.

I was running an adapter Thunderport to HDMI connected to my ASUS monitor. This was working flawlessly for long time. The 1st adapter brand was called Ivanky, the 2nd adapter brand was AmazonBasics, I am not sure of the all in one cable brand and I also have the Apple brand Thunderbolt to hdmi as per Apple support's suggestion.

I have tried these steps thus far:

1. Bought a new TB to HDMI adapter from Amazon Basics, the previous one was Ivanky. I was initially told that the OS update may have "fried" the adapter so I bought a new one. (unsuccessful).
2. Bought a new all-in-one standalone Thunderbolt to HDMI cable (unsuccessful).
3. Tried different HDMI cables that are known to be working on other devices (unsuccessful).
4. Tried different Thunderbolt ports, there are only 2 (unsuccessful).
5. Connected the Asus monitor to another Imac and laptop both MacOS (HS 10.13.3) and Windows 7/10 and the monitor works on those devices. Also works Xbox and Roku.
6. Connected a cheap but functional ACER monitor using same methods (unsuccessful).
7. Did the Ram reset (unsuccessful).
8. Did the SMC reset (unsuccessful).
9. Looked for an ASUS monitor driver update for Mac but one doesnt exist.
10. Updated the Thunderbolt DisplayLink drivers (unsuccessful). from here https://www.displaylink.com/downloads/file?id=1251
11. Removed the monitor completely from display prefs and restarted computer with and with out monitor connected on both ports several times, using a combo of the dongles and the cables (unsuccessful).
12. Reinstalled the OS (HS 10.13.6) and tried all of this again (unsuccessful).
13. Contacted Apple support and was instructed to again reinstall HS 10.13.6, which did not restore functionality. and then was instructed to update to Mojave and try all of the steps again (unsuccessful).
14. Contacted Apple support again after Mojave update was complete and was told to buy a new Apple brand dongle adapter (now, I own 3 adapters, also unsuccessful). But these adapaters work on other Mac machines, an older Imac with HS 10.13.3 and a Macbook.
15. Completely started over this process again from the beggining and was (unsuccessful).

Notes/ Symptoms:

The external monitor when connected shows "No HDMI signal" message on the screen. Which is the default ASUS message. The internal monitor on the iMac works fine. The external monitor doesnt flicker or display anything from the computer when connected to the mac. I mention this because some users reported flickering screens or jarbeld graphics or the screen suddenly going to sleep. I dont see these issues.

During these reboots & reloads, sometimes I can get the monitor details to appear in display preferences, but the detect display function doesnt do anything and since the Mojave update it no longer detects the monitor at all.

Now I am entirely frustrated because this is my work machine, and I cannot use my external monitor which affects productivity. I work in a fast paced graphics dept. of a publication company and need more than one monitor to work efficiently. This has been going on for at least 2 months or more and I am going crazy.

.....and the windows guys with their flawless quad monitors are now mocking me...I have screen envy and it's affecting my performance. I know, I know, "it's not the size of the monitor but how you use it"....but lets face it fellas, size and quantity matters. The office girls are also snickering, they dont think I can hear them but I can hear you JUST fine KAREN!

Notes:

Other devices like a Lacie HD connected to the TB ports work fine and as I mentioned everything was working perfect on this machine until the update to High Sierra 10.13.6. Previously I was on HS 10.13.3 or maybe 10.13.2 and now I am on Mojave. 10.14.2.

Apple support states that they are unaware of the issue being widespread and must consult their engineers. This computer works extremely well, fast and usually very solid. I am afraid they are going to tell me to buy a new machine which is out of the realm of possibility.

So I am turning to the community for help. Any suggestions would be welcomed.

I just want to be able to run multiple monitors again.

Help.