In this case, a workaround that you can use to turn off the start page is to reopen after closing the solution.
The following steps are listed below:
1. Close all instances of VS and Run Regedit
2. Select HKEY_LOCAL_MACHINE
3.File β Load Hive ...
4.Open% LOCALAPPDATA% \ Microsoft \ VisualStudio \ 15.0_ \ privateregistry.bin
5. Enter a name like "MyVSHive"
6.Find in HKEY_LOCAL_MACHINE \ MyVSHive \ Software \ Microsoft \ VisualStudio \ 15.0_ \ StartPage
7. Create a new dword with a non-zero value:
"DisableOpenOnCloseSolution" = DWORD: 00000001
8. Select "MyVSHive" and then go to "File-> Unload Hive" ...
9.Restart VS
Now, when you close the solution, the start page will not open automatically.
Note that resetting this will cause this parameter to be reset, and you will have to complete these steps again.
Thank,
Pravein [MSFT]
Worked for me. Copying in case this helps someone else.