Thanks for your reply! What you're suggesting was clear from the start. But this is not the most convenient option, You know. For example, if the user menu (both buyer and seller) should be located in one modular Joomla position. If both buyer and seller are located in registered, then both menus will be available to everyone (the seller can see the buyer's menu, and the buyer can see the seller's menu).
Only if you create a separate user group, you can solve this problem. A separate group will help you use the user group selection when registering on the site.
Maybe you had thoughts of doing something like this? Or there is a hint - how to determine the rights to manage the store only for a special group of users?