Possible to upgrade OS in 2015 iMac?

Hi Friends

My old iMac works great and I want to give it to a friend.

I deleted my data, but I think I deleted too much.

Now the iMac won’t upgrade anything.

When I try to go to the Apple upgrade page, the page won’t show properly. (Please see image.)

Maybe I deleted the Safari version that works today.

Is there a workaround so that I can get this iMac up to its latest compatible OS?

It was running Sonoma before I deleted data.

Now it won’t upgrade past Mavericks.

Thank you!