Hi @angelgarciamula3-del , welcome to github. I think your problem is more a question for the forum (forum.joomla.org) than an issue in Joomla. There is also some missing information. Can you please add more details? Which category dropdown? It is a fresh installation or an update? Do you have errors in your browser console?

Hi, this happens to me in all categories. It was happening in Joomla 4.4.1 and I updated to 5.4.1 and it's still happening in 5.4.2. When I create a new article, I choose a category to define it, and the dropdown menu of categories appears, but when I select one, it doesn't save. I have to move the article using batch processing. It also affects my Phoca Cart store; I can't select a category there either. This is happening across the board. It's the first time this has happened to me; I've been using Joomla since version 1.0.15 for several years. Thanks for your time.

Summary:
When creating or editing an article in Joomla 5.4.2, the category dropdown appears and shows all available categories, but when a category is selected, it does not display visually as selected in the form. However, the category IS saved correctly in the database (confirmed via SQL query).
Steps to Reproduce:

Go to Content → Articles → New Article
Click on the Category dropdown field
Select any category from the list
The dropdown closes but does not show the selected category name
Save the article
Check the database: the category IS correctly saved in #__content table (catid field)

Expected Result:
The selected category should display in the dropdown field after selection.
Actual Result:
The dropdown appears empty or shows no selected value, even though the category is saved correctly in the database.
Additional Information:

Joomla Version: 5.4.2
PHP Version: [pon tu versión de PHP aquí]
Database: [MySQL/MariaDB y versión]
Browser tested: [Chrome/Firefox/Edge - pon el que uses]
All categories are published (published = 1)
All categories have public access (access = 1)
Cleared cache multiple times
Tested with different browsers
Tested in incognito mode
Disabled third-party plugins
Reinstalled com_content component files
No JavaScript errors in browser console

Workaround:
Using batch operations to assign categories or editing articles after creation.
Database verification:
sqlSELECT id, title, catid FROM #__content ORDER BY id DESC LIMIT 5;
Shows that catid is correctly saved.

I can't reproduce the problem.

Have you checked the CSS? Maybe some definition is changing the color of the selected element ...

My screenshots:

can someone please add the information required tag to this issue

@angelgarciamula3-del Have you checked the console for js errors? Changing the category needs js, if there is an error, it cannot work.
This can be caused by any other plugin of any extension.