A lock icon on screen
After installed Ventura 15.3, my iMac run ok even slow. But when I update it to Ventura 15.6, then iMac stuck couldn’t boot up. I tried to use combination keys, not work, and a lock icon appeared on screen. I want to bring my iMac to Apple Store where I bought it 7 year ago, to fix, but they someone said they ask for receipt which I lost. What should I do? Thanks.
iMac 27″ 5K, macOS 13.5