IMac updates

See the following Apple articles:

Check the status of your network on Mac

Check the status of your network on Mac - Apple Support

If your Mac isn't connecting to the internet over Wi-Fi

If your Mac isn't connecting to the internet over Wi-Fi - Apple Support

If you can't connect to the App Store, iTunes Store, or other Apple services

If you can't connect to the App Store, iTunes Store, or other Apple services - Apple Support

-> If you tried all of the above steps and you still can’t connect, contact Apple Support.

Q - " checking for updates”

A - Updates as in Big Sur 11.6.4 to Big Sur 11.7.4 latest version

A - Or UpGrade as in Big Sur to Monterey or Ventura

For updates specifically >>

There are factors:

1 - Like poor Wifi connection

2 - Slow wifi connection

3 - Too many other people downloading at the same time and Apple Severs are overloaded

4 - Software on the computer interfering with the download process including AntiVirus Software

Notation: Disabling the AV Software may or may not solve the issue. Removal of the AV Software may increase the chances of the download to perform as expected.

5 - Running behind a VPN which may increase Packet losses or corruption of the download 

6 - If via wifi too many Other devices using the wifi at the same time reducing the Bandwidth to your computer. 

7 - Best Results are via Ethernet Cable to Router

8 - Restart in Safe Mode. This will perform a Disk Repair, clear cache files and only load Apple Software, extensions and fonts. The boot up will be slow and can take some time - Normal and Try Again using the Software Update Applet in System Preferences

9 - Worst case - Restart in Recovery Mode and choose Reinstall macOS. This in theory will pull the latest version of Big Sur available and commence the installation.