UnderTime allows you to place a customizable date underneath the time in the iPhone X's status bar.

See the top-left of the screenshot below

Changelog:

1.3: Fixed duplicate date bug, added option to customize first line of text, option to customize single line of text, option to use plaintext

1.2: Added many customization options (Font size, replace date option)

1.1: Inital Release

MPG13's repo