Can I install these other updates and not Big Sur?

Yes. If you click the Install Now button with the information open as you show it, only the Safari and Security updates will be applied.

Welcome, technology today, to Apple Support Communities!

You ask “Can I install these other updates and not Big Sur?“, referring to the Catalina Security and Safari updates.

Yes. You most certainly can.

You do not have to take the offered Big Sur upgrade! (In fact, that upgrade would make the other updates mute, null and void.)