The default digital clock settings and its current behavior can be distracting. The relevant settings are:

Time display: Use Region defaults
Date format: Short Date


In my case the resulting display can be:
4:01 P.M.
9/02/21

In another time it might be:
10:34 A.M.
9/02/21

The time line is much longer and thus determines the widget width. That can be a problem because some digits can be thinner than others, or a second hour digit may appear or disappear. These factors account for different total text widths that can change per minute or hour. A variable digital clock widget can and does displace the neighboring widgets such as a system tray, present in any default Plasma desktop.


EXPECTED RESULT
The digital clock widget should reserve space for varying width time display lines.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Debian unstable
KDE Plasma Version: 5.20.5
KDE Frameworks Version: 5.78.0
Qt Version: 5.15.2