1.
About forum home page, how to match Joomla menu item with EasyDiscuss home page (the menu with icon house)?
For Joomla menu item I chose “Forums Layout” item type without selecting a category so it will displays all categories, but if I click on EasyDiscuss home page I have a completely different display, indeed URL is also different, …/forum for the Joomla menu item and …/forum/index for EasyDiscuss menu item, how to have only one selected? ...otherwise in my opinion it confuses the user.

<a href="<?php echo EDR::_('view=index');?>" class="o-nav__link ed-toolbar__link">

<a href="<?php echo EDR::_('view=forums');?>" class="o-nav__link ed-toolbar__link">

2.
Is it possible to prevent a user to create its own tag, but rather to select available tags?

3.
I guess tags are not available in search filtering?

4.
How to prevent a registered user from not closing his post with “Resolved” option, only a moderator can close posts.

5.
About subcategories display, is it possible to have subcategories displayed directly next to the main category instead of having them displayed in a popup menu?

1.
I tried to create an override in /templates/my_template/html/com_easydiscuss/themes/wireframe/toolbar/default.php but it's not working, should I add more files in com_easydiscuss folder?

4.
Is it possible to leave only "Site admin" and "Category moderator" as unique users who can mark the post as “resolved”?
5.
Since I'm not a developer maybe you can tell me how to modify this file in order to make subcategories visible?

Yes, you are right, it is difficult to let the user know what is that category icon means if view the categories page on the mobile.

I will log this into our issue tracker and see if we can do something about it.

... please make it simple, without artifice, just display subcategories directly...

We totally understand that everyone has a different way of thinking about the same thing and the most tricky part is the difficulty to fulfill everyone's needs, I will bring up your concern to our designer regarding this and see if we can come out with a better design for this.

... both solutions are ok for me, thanks

Great suggestions and I also vote for solution 2 with focus on mobile view easy to use and understand.
We also have to think that some people have a l o t of categories and some just 3-4 and thats have a huge impact on how you solve these problems. If your site and categories grow with many translations you have to consider a smooth scrool and overview how this works with its best UI/UX for people that is not so skilled to use these systems.

Either way, I hope that you guys can use https://stackideas.com/voices/easydiscuss in the future to submit your suggestions instead of posting it on the forums as you guys are putting my team members in a tough positions.

and anyway with some CSS rules we can make the display pleasant

5.
About subcategories display, is it possible to have subcategories displayed directly next to the main category instead of having them displayed in a popup menu?

Unfortunately, we do not have an option to render subcategories on the page, but you can modify on this file JoomlaFolder/components/com_easydiscuss/themes/wireframe/helpers/card/category.php

I will get over this in a while (maybe) but at the moment I'm just disgusted...

Finding / adding icons to 420 forum categories is just a waste of time now.
These icons and images you can attach to categories do not have any purposes anymore

use svg icons ?

Hm, it still works on the desktop, so I do not think it is completely useless.

Hm, it still works on the desktop, so I do not think it is completely useless. This issue was raised by Lorenzo as their users find it difficult to view the subcategories on mobile browsers.