Rulers and Gudes work fine for me in Premiere Pro CC 2021.
I would suggest to reset the Premiere Pro Preferences -
Press Alt (Windows) or Option (Mac OS) while launching Premiere Pro. You can release the Alt key or Option key when the splash screen appears. To reset preferences and plug-in cache at the same time, hold down Shift-Alt (Windows) or Shift-Option (Mac OS) while the application is starting. Release the Shift-Alt keys or Shift-Option keys when the splash screen appears.
Vishu Aggarwal Adobe Certified Instructor, Professional and Expert