As you can see from the above image the network Icon at the right side of the battery icon is missing. This happens when I am on airplane mode for sometime. Does not happen when connections are active though.
Please point me to the correct category if this is not the right place.
Laptop: Dell Inspiron 3558
DE: KDE Plasma 5.15.
My link was related to updates, it was not possible to know if you had only 4 packages for updates or more ...
Since you have your system updated then we can look elsewhere for your issue.
Does the network icon becomes visible when you exit the airplane mode? Do you use LAN and WIFI together? Turning one of them on and off makes a difference? Logging on and off makes a difference even if both are active?