Product:
Planning Analytics 2.0.x – 2.1.13
TM1 Architect
Issue:
How can i set a WEBSHEET page as default for all people who login to TM1WEB?
Solution:
Create a websheet and publish it as public, under a folder in your applications, from TM1 Perspective or PAFE.
Then go into TM1 Architect as Administrator.
Right click on your TM1 instance/application and select security – clients/groups
In the dialog – click on Settings.
At homepage – click on browse and select the websheet you want to use.
At apply to select All Clients.
Click Apply settings.
Click OK.

Now this page will show for all users when they login to the Application in TM1WEB.
If you change the websheet in any why, you need to repeat above steps, as this setting is lost when you publish a new websheet.
More Information:
IBM Planning Analytics Tips & Tricks: Custom landing pages for TM1 Web
https://code.cubewise.com/blog/the-revenge-of-tm1-web/
IBM Planning Analytics Tips & Tricks: Application Websheet Folders