You can check if Apple servers are experiencing issues. It is possible that Apple servers are overloaded as a lot of people may be trying to update. Apple can make calls like this based on how many people are still using the software and how severe the security issues are.
In November of 2020, Apple issued a security update for macOS High Sierra, even though it was three versions behind the latest release (Big Sur) at the time. Or there could be issues with Apple servers. Sometimes, Apple will update versions of macOS that fall outside of the two-year cutoff.
If you are using a Wi-Fi connection, try a wired connection, if possible. You may want to restart your router and modem to fix this problem. Then click Update All or Update next to individual apps. If you want to learn about the details of each update before installing, click the arrow next to the Update button and review the apps, versions and installation date.
You may have a slow internet connection. Click Update to download and install all the available updates.It is possible that your Mac may unable to reach the update server.To reset PRAM, turn off your Mac and then turn it on and immediately press and hold the Option, Command, P, and R keys together for about 20 seconds. msupdate -install -apps XCEL2019 -t 180 -m 'Excel will close in 3 minutes to install updates.