Your footer here shows an iMac Pro, and that’s not available as a 2011 model.
If Safe Mode gets you nowhere… Build yourself a hardware test disk, and boot that and see what the hardware test reports.
The following has links to downloads available from Apple for various iMac models:
https://github.com/upekkha/AppleHardwareTest
Given the vintage and the report, quite possibly a failed hard disk.
It’s possible to boot and use external storage, but the external I/O on the iMac 21.5” 2011 is pretty slow. The other iMac models from 2011 have Thunderbolt, which is decently fast for the era but will require purchasing a Thunderbolt external storage device and those can be somewhat more expensive. USB 2.0 is, well, slow.
Hopefully you have a complete and current backup.
If you do not have current backups, STOP ACCESSING THIS DISK RIGHT NOW—and decide if you want to pay for data recovery. If you do, messing about more with a failed hard disk—whether Safe Mode, or diagnostics, or attempts to reload, whatever—can potentially reduce what data can be recovered, as hard disk failures can tend to be progressive. If you don’t want to pay for recovery and have no backups, you can try getting a backup from Recovery, or using Target Disk Mode. Do that backup first.