clocksaver is a screensaver for MacOS 10.15 and onward. It is designed to have as minimal CPU use as possible. It simply shows the time and the date. Nothing more complicated than that.

Download clock-saver-source.zip source code
Download clocksaver.zip
Here's an updated one. In Sonoma, Apple removed the "Screen Saver Options..." button from System Settings. Third-party screensavers can no longer display their configuration sheets through the standard UI. To get around this, you can click the preview of the screensaver in the preference pane to get at the configuration dialog.
Download clocksaver-sonoma.zipOnce installed, colours are customisable too:

If you have any suggestions, please get in touch via email. Many thanks.
Tom.
tom@tsites.co.uk