How to make a static homepage in latest version of joomla?
How to restore trashed categories? I can't load the site, saying category not found, although i don't need the category
To make a static homepage, create the article for the homepage, then change your homepage menu item to single article menu item and select that article for your homepage. - Procedure is the same as in older Joomla versions, if you are familiar with them.
To Restore trashed categories, go in Articles - Category Manager, click the Search Tools, to display the filters, then use the status filter to display either all, or trashed categories. Select them all and click the Publish button from the Toolbar, to set them all to published.
However the Category Not Found error page, may not necessarily be connected with trashed categories. It may simply mean that you link to content that is for whatever reason not available. If this occurs in your home page, then go in Menu Manager and check your home menu item type and where it links to.
@Lynob: for comment:
What I did to make homepage is use the redirect, from index.php to static page, is that what you mean?
No, it's not what I mean. Static pages in Joomla is term used for long time to describe pages that display a single article and not content that will be changed like a blog category or list of articles of a category. So, that's what I understood when you said static pages in Joomla. What you are after is to have a static html page (that's not a Joomla thing).
For solution on this read here: How to make external url as homepage