Big Sur update hangs

I am trying to upgrade to Big Sur. Download and verify went fine, started update. Projected time was “about28 min”. About 26 min in, the update hung, after five hours nothing had happened. Still have the Apple logo, time bar with about a quarter inch remaining. Can’t restart to try safe mode or any of the other recommended solutions. Tried the power button, put screen to sleep but when stared again I have the same screen. What action?