You can't. MS dramatically reduced the ability to customize the shell in Win11. My assumption is that they did it to enforce a UX that they wanted without having to worry about all the flexibility you used to have.
Beyond determining top or bottom of screen and whether to use small or regular size taskbar you really cannot customize the UX. Some registry entries may work from Win 10 but they are not supported and can break during an update.
An alternative is to use a third party product to restore some of the functionality. Startdock's Start11 does a pretty good job of restoring some of the customizations and look and feel from Win10 but it is still limited to what is available. For example you can restore the Win10 taskbar look and feel but you are still limited to the top/bottom of screen and you cannot resize it. Beyond that you can provide your feedback to the Windows team using their feedback hub tool and perhaps they will consider restoring the functionality.