So I would like to create some KAlarm templates so I can re-use some alarms.
I am running KAlarm Version 3.0.0 (KDE Apps 20.08.0) according to the 'About KAlarm' window.

When I go to File -> Templates..., then press New -> Display Alarm Template and create any kind of Template, I can see that the template is indeed created in the templates.ics file.

However I cannot create an alarm from that template.

1. File -> Create Template... is greyed out and cannot be clicked.
2. Pressing New and hovering over New Alarm from Template does not show any alarm. Clicking also does nothing.
3. Clicking New -> New Display Alarm opens up the dialog to create a new alarm, but the button at the bottom that says Load Template... is greyed out.

Other indications that something is wrong:

1. Clicking View -> Show Calendars and then Selecting Alarm Templates shows that the default Calendar (Alarm Templates) is checked but no actual templates are shown on the right side of the KAlarm window.
2. Using akonadiconsole shows that there is no Agent registered for KAlarm. I have already tried to make an Agent from a KAlarm Directory (and pointed it to the folder where I found the templates.ics file) and then redid the things mentioned above, but with no change in result.
3. Going to File -> Templates... and removing a Template there, creates a pop-up error window with the message "Error saving alarm template"

I've replicated the fault which you found, so it's definitely a bug - I've raised a bug report at https://bugs.kde.org/show_bug.cgi?id=425751 to enable it to be tracked. I'll make sure that it's fixed for KDE Apps 20.08.1.

Please note that KAlarm no longer uses Akonadi (although it's still possible for other applications to access KAlarm calendars via Akonadi). So creating an Akonadi agent won't affect KAlarm. I'd recommend that you remove the agent which you created, since it will use system resources for no purpose.

Also note that clicking View -> Show Calendars and then Selecting Alarm Templates isn't designed to show individual alarm templates - its purpose is only to enable listing, adding or removal of alarm template calendars. The right hand side of the window should still show the alarm list as usual.

File -> Create Template is supposed to be greyed out if no alarm is selected. If an alarm is selected it is enabled and opens the edit template dialog based on the selected alarm.

The remaining items are now fixed for KAlarm version 3.0.1, to be released in KDE Apps 20.08.1.

Thanks a lot for your quick response.

I absolutely love KAlarm because of how useful it is, glad I'll be able to make full use of it again.