The interface theme is not saved

Hello @Mickhael355167071r7i,

We understand that encountering technical issues can be frustrating. Would you mind trying to manually reset Illustrator's preferences and checking if it helps:

For macOS

• Close all Adobe applications.

• Go to the following locations

• ~/Library/Caches

• ~/Library/Application Support/Adobe

• ~/Library/Preferences

• Rename Adobe Illustrator, com.adobe.illustrator and Adobe Illustrator 28 Settings folders to Adobe Illustrator.old, com.adobe.illustrator.old and Adobe Illustrator 28 Settings.old

• Launch Illustrator from the Creative Cloud.

Note: Location starting with this "~" sign indicates the User Library, which is hidden. So, you need to copy & paste the exact path in spotlight search or from Finder Menu > Go > Go to Folder > Paste the location in the dialog box like this:

For Windows

- Close all Adobe applications.

- Go to Location C:\Users\%USERPROFILE%\AppData\Roaming\Adobe

- Rename Adobe Illustrator and Adobe Illustrator 28 Settings folders to Adobe Illustrator.old and Adobe Illustrator - 28 Settings.old

- Relaunch Illustrator from Creative Cloud

Disclaimer: Please note that renaming preferences folders will remove all the custom settings, and Illustrator will launch with default settings. You can also save a backup of the folders in case you want to. The location is mentioned above.