To flesh out the steps given by others, see the attached screenshot of Attribute Manager. For speed, there is only one image, but unfortunately the names on the buttons change after you do certain steps...
Back up your file first!
Click the Open button (shown as Close here) to open the default AC 11 template from within your program folder. If you cannot find it, just open a new project 'from template' and save it, then reopen YOUR project, and in this dialog open the empty project that you created from the template.
Switch to the Fill tab as shown. You'll see all of the template fills on the right, and you'll see the 15 lonely fills left in your project on the left.
Click one fill on the right and then click the Select All button (which reads "Deselect All") at the moment.
Then, click the <<Overwrite button to copy all of the template fills into your files at exactly the same index numbers. It is the number that matters, not the name.
Finally click Apply.
You might want to go through the other tabs - such as Materials - to see what else got deleted from your file and restore it the same way.
If someone mucked with your file in a way to move standard attributes into nonstandard index numbers, then the direct process above will result in your model not appearing correct. Someone else can post the more complicated steps if that is the case...
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB