https://arstechnica.com/gadgets/2022/03/a-mixed-bag-of-windows-11-beta-updates-includes-hidden-file-explorer-tabs/

Microsoft is testing a tabbed interface for the Windows 11 File Explorer, according to screenshots from developer Rafael Rivera. You can't access the feature without changing hidden settings in the latest Insider Preview build for the Dev channel, but XDA Developers has published a guide on enabling the interface. The process involves downloading ViveTool, a utility that has been used to dig up other present-but-hidden features in Windows preview builds.

Microsoft briefly tested File Explorer tabs in Windows 10 but never ended up including the feature in the publicly released version of the OS. We'd expect the tabbed File Explorer interface to be formally introduced and enabled in a future Windows 11 Insider build, as we saw in the redesigned Task Manager and a few other UI changes that have been discovered before they were announced.