Hi Joomlafans,

Where can I find the style sheet file or default.php or html file in order to adjust the layout of EasyDiscuss main posts and Category lists?

For EasyDiscuss main posts, which layout are you referring to? Forums or Recent?

For all categories listing, these theme files are responsible.
JoomlaFolder/components/com_easydiscuss/themes/wireframe/categories/default.php
JoomlaFolder/components/com_easydiscuss/themes/wireframe/categories/default.item.php

How Can I hide the responsive hamburger menu and instead only display the Categories menu item next to (ask a question) button and search in the mobile/responsive toolbar?

You would have to template override the following toolbar theme file.
JoomlaFolder/components/com_easydiscuss/themes/wireframe/toolbar/default.php

This part is responsible for the hamburger menu(https://i.imgur.com/wGLZU7Q.png). You can place your categories menu item code somewhere in this part(https://i.imgur.com/GqlaVDc.png) depending on where you want it.

In case you are not familiar with template overrides, here is the documentation.

Basically you need to use this override method when overriding theme files so that your changes are protected from future updates.

That worked like a charm.

Thanks a lot Raymond

You're most welcome Joomlafans.

Just for your information, I have locked and marked this thread as resolved to avoid confusions in the future. Feel free to start a new thread if you have any other issues.

Regards.