Turn Off Salesforce Classic - Only Lightning #inSalesforce

If users are now comfortable with lightning which has more advantages and you want users to fully switch to lightning, you can switch off classic.

Steps:

Setup in Lightning Experience | Lightning Experience Transition Assistant. | Select the Optimize phase. | Click Turn Off Salesforce Classic for Your Org to expand the stage. | Turn on Make Lightning Experience your org’s only experience. 

Now onwards, Users see Lightning Experience the next time they log in to Salesforce.

Reference: https://help.salesforce.com/s/articleView?id=sf.lex_turn_off_classic.htm&type=5