Can't select Software Monitoring Feature

Yes, I guess you are not using an audio interface?

Are you using the built in mic?

This is a safety measure when using built in microphone in conjunction with the built-in output.

Try plugging some headphones, that will fix it.

Software monitoring wont be greyed out then.

Make sure your audio devices are set correctly in Logic's Preferences/Audio/Device

Next try the Menu command (under Logic Pro) "Reset User Preferences Except Key Commands". You will need to reset several your uses prefs after using the command, or by going extreme and deleting User Prefs. Make note of what prefs you've changed before performing either operation. (Note:) the Restart is important.

Delete user preferences

Before deleting user preferences, note any specific preference settings that you’ve made, and save any custom key commands you've created. Deleting preferences removes any custom preference settings and custom key commands.

To delete the user preferences, do the following:

1. Quit Logic Pro X.
2. In the Finder, choose Go > Go to Folder.
3. Enter ~/Library/Preferences, then click Go.
4. Remove the "com.apple.logic10.plist" file from the Preferences folder.
5. If you upgraded from an earlier version of Logic Pro, also remove the "com.apple.logic.pro" file.
6. Restart your Mac.

Try this:

check the little downward arrow on the bottom right of the control bar

Then choose Customise control bar and display

Then check software monitoring

The software monitoring should appear at the top.

See if that sorts it!

Good luck

May I ask what version of Logic you are using?

thanks in advance.