Can't seem to update from Mojave

I want to get os 11 or higher. I tried upgrading to Ventura from sys prefs, and it showed the progress bar as if it was upgrading, but then the progress window/modal disappeared with no other information displayed. I restarted the computer, no change, still running Mojave. Then I tried upgrading to Big Sur from the app store, same thing happened. I assume my system is not adequate, but then shouldn't Big Sur be greyed out in the app store? I am now running: macOS Mojave Version 10.14.6 (18G9323) iMac (Retina 5K, 27-inch, 2017) Processor: 3.4 GHz Intel Core i5 Memory: 8 GB 2400 MHz DDR4 Graphics: Radeon Pro 570 4 GB