iMac 2017 stuck at less than 1 minute remaining in Monterey install

This seems to be pretty common - question has been asked many times in many forums, but not often on Apple discussions. This 2017 iMac is absolutely standard. The install has been stuck with progress bar and the "less than 1 minute remaining" message for 40 minutes now. Does anyone have experience of:

1. Whether it will resolve itself if left for long enough?
2. What happens if I do a hard power off (hold the power button for 5 seconds). Do I end up with Monterey, or the previous install, or a brick?
3. Any other solutions?