If you are looking for a good client for Mastodon on KDE neon then Whalebird is an Electron based Mastodon and Pleroma client for Windows, Mac and Linux. It’s quite good and looks a little like the Slack UI. The website can be found here.
To install Whalebird on KDE neon go to the website and download the Whalebird 2.7.1.deb (64bit) (or whatever the deb version is at the time), right click on it and select open with Discover. This will open the deb file in Discover for installation. Select install at the top right to install it. You will have to enter your password.
After installation you can find Whalebird in your Applications Menu by either searching for it at the top or by going to Applications/Internet.
Tips and Tricks
When you open Whalebird for the first time it will ask you what instance you wish to join. Assuming you already have a Mastodon account then the instance is the last part. So if my account is @firstname.lastname@example.org then the mastodon.social part is what you want to use.
After that it will take you to a web page and ask you if you want to authorise the app and then give you a secret to paste back into Whalebird. That is pretty much it. After that you are all set.