2017 iMac can't start up, freeze at apple icon and half of the progress bar.

Regardless of the details displayed during each run, if Disk Utility finally reports the volumes, containers and startup drive have passed, then you can quit DU and attempt another normal restart of your iMac. With luck this will get you past the stall and back into the computer. 🤞🏽🍀

If the Mac still refuses to boot properly, then you might consider taking advantage of another Mac to access the internal drive via Target Disk Mode. Otherwise, things get more difficult and complex.

Please see: Transfer files between two Mac computers using target disk mode - Apple Support

Will the iMac startup in Safe Mode, as per > How to use safe mode on your Mac - Apple Support

If not, see > If your Mac starts up to an Apple logo or progress bar - Apple Support

Sadly if the drive has failed without a backup, then it maybe too late.

Boot your iMac in Recovery mode, and then use Disk Utility to run First Aid again.

To do this properly, you must enable View > Show All Devices in Disk Utility, then run First Aid on each indented Volume, Container and then the startup Device (topmost device), in that order, until each run passes.

Please remember when starting in Safe Mode this type of startup should be done with a wired keyboard, you can plug in the charging cable for your keyboard and that will make it wired. Also, continue to hold down the Shift key until the computer starts up, this can take up to 5 minutes.

Also, going forward never operate any computer without a sound backup plan. Without backup you are playing Russian Roulette with your data and eventually you lose. At the very least you should be using Time Machine to backup to a dedicated External Hard Disk.