For CD side it is easier, all DB related info is located in cd_storage_conf and deployer-conf files. After update just restart microservices.
For CM side it is a little trickier since DB related info is encrypted using Tridion Rsa key.
CM DB info is located in %TRIDION_HOME%\config\Tridion.ContentManager.config
Topology Manager DB info is located in %...
After some more research, it turns out that a previous failed install was causing this problem.
The previous install had placed some files, but most likely not everything.
We were able to fix it by first uninstalling the failed installation, and then running the unattended install again.
Yes. It's possible to Configure Add-On Service on the Content Manager side to install the SDL Tridion Sites by scripted to install silently then it is required to pass
Indeed, The documentation it was missing, I will raise this internally to update the documentation, also left the comment in the documentation section.
AFAIK - SDL Tridion Sites 9.1 - you need to manually install the .Net framework 4.8 and .NET Core Runtime 2.2 manually prior to install.
Note: These pre-requisites not comes with SDL Tridion Sites installation media.
This is solved now. It was a bad combination of Windows server roles.
First, we had the Domain Controller Role in our server.
(more information in Topology manager not installed: Authorization denied)
In a different installation, server was not a domain controller but we had a problem with IIS.
Finally we found the right setup for our Windows installation ...