Management Action - macOS 10.15.7 Catalina showing Important Update alert

Today I got this alert window as the posted pic below. By clicking Submit, there's no response or restart automatically. I tried to restart manually the machine but a few moments later, it pops up again. Is there anyone who can help on it?

That looks a lot like the Management Action dialog that Jamf's device management systems use (see here for an example). Is your Mac being managed by some company/school/etc you're associated with? If it is, it's probably the remote management admin "encouraging" you to install Security Update 2021-006 for Catalina, which just came out last week and does indeed fix a critical vulnerability.

Since it doesn't seem to be working properly, I'd recommend just going into the Software Update pane in System Preferences, and running it from there.