We would appreciate it if you could add S Calendar from the iPhone widgets addition screen.
For adding or changing widgets, please refer to Apple's support site below.
▼Apple support site
https://support.apple.com/guide/iphone/add-widgets-to-the-home-screen-iphb8f1bf206/ios
Also, if the set widget is not updated, please delete the widget once, restart the iPhone, install the widget again and see how it goes.