You’re analysing C# code, so you’ll be using either the SonarScanner for .NET directly, or indirectly via the SonarQube Azure DevOps extension. Either way, the analysis pipeline will have three steps: begin, build and end (in the Azure DevOps extension begin = Prepare analysis and end = Run analysis). Each analysis run completely replaces the analysis results for the SonarQube project
If you are using SonarQube Community edition and want to report the results for multiple VS solutions in the same SonarQube project, you will need to build them both in the build step i.e.
1 - begin
2a - build solution 1
2b - build solution 2
3 - end
If you are using SonarQube Developer edition or above, you can analyse the projects separately but view the combined results on the server as an “Application”. See the docs for more information.