Thank you for your reply Robert,
The data that I use from the .odc connection is the main reason for my project. If I remove that data, I have no project. 🙂
I can't move to version 3. I run a lot of Python scripts on the 2 machines that I have available and 3 will most likely break the scripts. Upgrading the scripts will take a while.
I opened a case with ESRI and the analyst suggested to install .Net Framework 4.8.1 and remove patch 5, since I can't upgrade to 3. But, unfortunately, the installation of the framework was blocked with the message that it is not supported on this OS (Windows server 2019), go figure. So, that is not going to work.
I uninstalled patch 5 and I can open the projects.
Since my maps were imported from MXDs, I can, probably make all necessary symbology changes in ArcMap and import the maps to Pro after I am done. Then publish the services from Pro 2.9.4.
Hopefully, there will be a solution soon.