How to Remove Salesforce Classic Access and Disable the Classic Switcher for Your Salesforce Org

This article provides steps to disable Salesforce Classic access for your entire organization and to remove the Classic switcher for specific users.

Disable Salesforce Classic for the Entire Org

1. In Salesforce Lightning, go to Setup.
2. In the Quick Find box, enter lightning, then click Lightning Experience Transition Assistant.
3. On the Optimize Phase, click the Go to Steps link.
4. Click Turn Off Salesforce Classic for Your Org to expand the section.
5. Toggle the switch for Make Lightning Experience your org's only experience to On.

Note: If you do not see the Lightning Experience Transition Assistant, the "Lightning only" permission has already been selected.

Limit Classic Access for Specific Users

You cannot remove Salesforce Classic access for specific users if they have the View Setup and Configuration permission enabled through custom profiles or permission sets.
If your organization uses standard profiles, create a Permission Set with the "Hide Option to Switch to Salesforce Classic" permission enabled, and assign it to the relevant users.
Refer to Salesforce Help: Hide Option to Switch to Salesforce Classic for details.