My company has completed conversion to Lighting and disabled Classic for all users. This tab still shows in the Object Manager. I haven't found a way to remove or disable these layouts. What's the process for that?
This question relates to my recent post about lookup layouts. I'm not sure if the existence of this tab and the layouts on it are what's causing lookups to appear like Classic.
As confusing as the name is, the Search layouts for Salesforce Classic tab is used for updating the List View Layout which applies to both Lightning Experience & Salesforce Classic. As of now, this tab will continue to display to provide that functionality.
This is mentioned in Customize Search Layouts for Custom Objects under Other Layout Options
In Lightning Experience, you can select Search Layouts for Salesforce Classic. This option lets you easily access layouts for Salesforce Classic without switching out of Lightning Experience. Layouts include: Lookup Dialogs, Lookup Phone Dialogs (for Salesforce CRM Call Center), Search Filter Fields, and Tab. This page also includes the List View layout, which unlike the other layouts on this page, applies to Lightning Experience and Salesforce Classic. Use the List View layout to add and remove the action buttons that users see on all the list views for a given object. For example, if you remove the New button from the account list view, that button is no longer shown on any account list view.
When you click on Edit for the List View layout, you're presented with a screen that has a section for List View Actions in Lightning Experience.
In terms of more background, Winter '20 brought a Lightning-only feature of Profile-Specific Search Results Layouts which created the Search Layouts tab you see now in Lightning Experience. This forced the other tab, previously named Search Layouts, to be renamed to Search Layouts for Salesforce Classic (even though list view layouts still affect LEX).
I took a screenshot from the following video (Summer '18) that shows the Search Layout tab used to display what is currently in Search Layouts for Salesforce Classic in LEX before that profile-specific search layout tab existed.
