The dialog "Checking for Updates" runs endlessly. (I currently run OS 11.7.4)

I understand Software Update is "Checking for updates..." with no end in sight.

Several workarounds have been proposed, such as restarting your Mac in "Safe Mode" and checking for updates while in that mode, and / or resetting NVRAM. Try both.

How to use safe mode on your Mac - Apple Support

Reset NVRAM on your Mac - Apple Support

Related: Software Update stuck at "Checking for updates"… - Apple Community

I am having the same problem after updating my Mid 2014 13" MacBook Pro to 11.7.4 - now "Checking for updates..." spins indefinately.

One thing I noticed was that if I boot into safe mode, then Software Update works - in fact it found and installed a Safari update.

As another diagnostic step, I made a second account on my laptop. Even in normal mode, that account can run Software Update and immediately get a response that my laptop is up to date with 11.7.4. So that led me to believe its something with my account and not safe vs normal mode.

I tried deleting softwareupdate plist file and rebooting, but that didn't help. So far I need to run software update from another account since upgrading to 11.7.4

"softwareupdate -i -a" also hangs in Terminal.

I checked my login items wondering what difference exists between my account and this new test account, and the only login items I have are dropbox and google drive

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.