You might find that when you have multiple browsers installed in KDE that even when you set Chrome as default, sometimes files or links open in Falkon or Konqueror or other browser you have installed. I noticed this happened recently when I sent a Chrome tab from my phone to my laptop using KDE Connect and it opened in Konqueror instead of Chrome, when everything else opened in Chrome.
Firstly check -
System Settings > Applications > Default Applications > Web Browser
You can use the filter box to quickly get to the right settings -
Secondly you can change default browser on the command line too, this is useful for doing this remotely or when you have multiple desktop environments installed.
As you can see I have Google Chrome set as default.