MyBB Community Forums

I upload themes via FileZilla, but they are not displayed in themes on the site. Maybe I did not fill them there?

compressed file of a theme should be extracted in your computer
& its contents should be used for the theme installation.

extracted theme mainly consists of 2 parts
- a folder with theme name & a xml file with theme name

folder with theme name needs to be uploaded to images folder of your forum files server

xml file with theme name needs to be imported through themes section of forum admin panel

below videos at youtube could be helpful in understanding MyBB theme installation
* How to install themes for Mybb
* Install New Theme In Mybb
* How to install a new theme or skin on MyBB

And if in the folder with the theme there is no file "XML", I downloaded it from your own site, from the topic download section.
https://imgur.com/BQMXYCh

looks like you have downloaded cerise theme for forum admin panel.

cerise theme for the forum is :
https://community.mybb.com/mods.php?action=view&pid=736

You appear to have downloaded the cerise acp style which would go like so:

forum/admin/styles/cerise

And then would need to be selected via acp preferences. Though note that the cerise acp style is outdated and if you want the latest version download cerulean acp style which has both cerulean and the latest version of cerise acp styles in one package.

Now, if you are downloading cerise frontend theme the directory structure is as follows:

forum/themes/cerise