NixOS Manual on desktop doesn't launch correctly

I installed NixOS with KDE Plasma on my laptop a couple of months ago and since then I have not been able to get the NixOS Manual in the Application Launcher to launch correctly. For some reason, it launches in KWrite.
Is it supposed to launch in a web browser? Because I think it is simply an .html file.
How do I fix this?

Just an F.Y.I. the default application set on my machine for .html files is Firefox.

Here’s a screenshot of the launcher:

For anyone else who comes across this issue using KDE, it is a bug here: 442721 – kf.service.services: KApplicationTrader: mimeType "x-scheme-handler/file" not found

The fix for me was this from comment 10 in that link above:

enable hidden files in dolphin then go to your home dir (/home/username) then go to hidden .config dir in there you need to find file named mimeapps.list edit it, add this string (x-scheme-handler/file=org.kde.dolphin.desktop;) to all sub strings for example:

[Added Associations]
.....
.....
x-scheme-handler/file=firefox.desktop;

[Default Applications]
.....
.....
x-scheme-handler/file=firefox.desktop;

then execute this command in the terminal: update-mime-database