Why my C drive is full? I don't install many apps

There will be pending and post system updates on the disk. You should delete them with the disk cleanup utility to free up the space.

Why don't you delete the worthless stuff.

Delete downloaded videos perhaps?

Windows 11 comes with a free disk clean app. You can use it to spot the junk and cache files.

How many apps you have installed on this device?

Use Disk Cleanup Utility: Search for Disk Cleanup from the Start Menu to remove temporary files, old Windows updates and unnecessary system files.
Manage restore points: Manage or delete old restore points to free up space by going to System Properties > System Protection > Configuration.
Clean up temporary files: Temporary files generated by browsers, installers and applications can take up space. In addition to using Disk Cleanup, you can use third-party tools such as CCleaner to remove these files.
Find and delete large files and folders: Check your C drive regularly and delete forgotten large files or folders to free up more space.