Hello,
You can customize the Widgets by just selecting some new ones in wp-admin > appearence > widgets > private files sidebar.
WP Customer Area adds some default widgets if the sidebar is empty. So, if you start adding any widget to the sidebar, it will remove the default ones and let you select what you want instead.
If you want to fully disable the sidebar, yes, you can use the code snippet you mentioned. Please take a look at the code snippets documentation to know where to place those snippets.
Regards.
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