osp realty template navigation problem

Basically, I created 3 languages and 3 menus - all is working correctly - but when I put them in the position "Mainnav" nothing happens. 
The template can select menu - and it appear only from theme edit options, but not from modules. 
That's bad, because I have to make 3 copy of template AND if I add another button to the menu - I have to go to template and press "Assignment" and select new button, so that template will be shown on it too, so I will be able to see the menu. 
If I don't do it - then on the new button there is no menu at all if you go there. 

SO I want to stop menu from the template and use from modules - how can I do that? 

Hi Sergey,
We have just released new version of OSP Realty template, new version of template supports Joomla 4 and Joomla 5, PHP 8.
You can upgrade your site to Joomla 5 and using OSP Realty template normally.
Thanks
Dam