Users cannot create a social network group

Are you using Joomla SEF? If so what settings are you using under "SEO Settings" in Joomla global configuration? If using 3rd party SEF there's nothing we can do about that as we don't support or test 3rd party SEF extensions.

I do not use third-party SEF extensions. Here is a screenshot of the settings Joomla.

I'm not sure what else to suggest. Still works fine in my tests. Also works perfectly fine on our demo site below.

demo.cbdemosites.com/

There's no reason for it to not work. The alias after the ID is entirely irrelevant and is only there for SEO. So whether it's 4-proekty, 4-project, or 4-blabla it doesn't particularly matter as it will always be using the category with an id of 4.

Only thing I can think of is maybe Joomlas language filter plugin is causing issues with the category variable in the URL. Try disabling it within Extensions > Plugins and see if issue persists.

I understand what's the matter!
When creating categories in the CB Menu, I wrote down the ID. In one of the categories, I indicated a non-existent ID.
Because of this, there were all the errors.

To fix the problem, I had to delete all the created categories, groups, and all menu items of the categories.
After that, I again created all the categories and groups, and then the menu items of the categories with the correct ID.

Moreover, I had to change the aliases of the categories in the menu, since with the old aliases the problem did not disappear, even after completely removing the menu items and cleaning the cache.
Also the error did not disappear: Call to undefined method: id

But groups are now being created. Thank you for your help.

Also the error did not disappear: Call to undefined method: id

Please check server error log or enable debug mode and maximum error reporting in Joomla global configuration then recheck the error then provide the file path for the error. Without knowing where the error is coming from there's not much I can suggest. There is no directly accessed id (e.g. ->id) calls in GJs router or its component file so I'm guessing that's not coming from GJ directly.