SUMMARY
When trying to create a new network connection configuration (WireGuard in my case), Network Manager (/usr/sbin/NetworkManager) throws an unnecessary error with connection names that are longer than 15 characters or which include certain allegedly illicit characters. It then closes, causing all work done configuring the connection to be lost.

STEPS TO REPRODUCE
1. Open Network Manager.
2. Create a new connection (WireGuard in my case).
3. Edit as desired.
4. Try to save the new connection.

OBSERVED RESULT
1. Network Manager closes the connection creation dialog box and eliminates all the user's work configuring the connection.
2. Network Manager throws an error through the Plasma notification system.
3. The error alleges that the connection name was too long or contained one or more illicit characters.

EXPECTED RESULT
1. Network Manager should not close the connection creation dialog box until either (i) the user enters acceptable configuration parameters and clicks on OK, or (ii) the user clicks on CANCEL. A bad field value should not auto-abort the configuration process with no chance to fix the error(s).
2. Network Manager should advise the user of the error through a modal dialog box that returns to the connection editor window, so that errors can be corrected, rather than forcing the user to start the whole process over from scratch.
3. The 15-character limit and the refusal to accept certain characters (space and "-", as far as I could tell) do not apply to pre-existing connections (Ethernet, WLAN, etc.) and therefore are assumed to be spurious limitations existing only in this part of the Network Manager code.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Kubuntu 20.04, kernel 5.4.0-050400-generic
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.68.0
Qt Version: 5.12.8