To publish to Tableau Server 2018.2, you need to use Tableau Desktop 2018.2. So, simply saving the workbook as 2018.2 will not help. Please download and install Tableau Desktop 2018.2 and proceed from there.
If I reinstall to 2018.2 will I be able to open my workbooks that have been converted to 2018.3?
No. So, what I would suggest is whatever workbooks that you have upgraded to 2018.3, please save them as 2018.2 workbooks first.
Note: You don't need to uninstall 2018.3. You can let it run on your system and install 2018.2 also. Only when you are opening Tableau, you just need to remember to open 2018.2 by default, or have a specific shortcut for that.
You are correct! I tried everything but found that I had to install the 2018.2 version in addition to my 2018.3.
It is my hope that you and anyone else reading this post vote for a feature to be added as desktop versions are upgraded to include a server downgrading feature.
This information was posted to my post on server administrators forum.
Please vote for the following feature request https://community.tableau.com/ideas/9380 so that we can downgrade published data sources just like we can workbooks and don't get stuck in nightmares like this.
Thank you, again for your assistance.
You are welcome, and I have also voted for your idea.