Segregating Vault Entries

To use tags like folders in the sidebar instead of the hardcoded categories in the desktop app, it's useful to activate the display of tags and disable the display of categories in the sidebar. Settings->Appearance. Now your two tags will appear in the sidebar on the left, and if you click on them, the list will be filtered accordingly. Don't use the "all items" category, use the tag for filtering.

"All items" will continue to contain all items, which is defined as the combination of all items in all your vaults in your account or in your current collection. If you want to make a part of your items completely invisible, sort them into vaults and create different collections for them. This will remove them from search results as well. However, this might be overkill. Usually, it's the easiest way for managing to keep all items in the same vault and only use the tags as filter.