kubuntu-desktop : Depends: software-properties-kde but it is not going to be installed

Try installing software-properties-kde and get

The following packages have unmet dependencies:
  software-properties-kde : Depends: python3-software-properties (= 0.96.24.32.11) but 1.8.8 is to be installed
 E: Unable to correct problems, you have held broken packages.

Try to install python3 from the bionic from bionic-updates

sudo apt install -t bionic-updates python3-software-properties

Install software-properties-kde

sudo apt install software-properties-kde

If it fails try force installing it

sudo dpkg -i --force-overwrite /var/cache/apt/archives/software-properties-kde_0.96.24.32.11_all.deb

Install Kubuntu desktop

sudo apt install kubuntu-desktop

More info here
https://pravin517.wordpress.com/2019/07/14/kubuntu-desktop-depends-software-properties-kde-but-it-is-not-going-to-be-installed/

Install KDE on Linux Mint 19.2

First add the following repo

sudo add-apt-repository ppa:kubuntu-ppa/backports

Make sure you are updated and upgraded

sudo apt-get update && sudo apt-get dist-upgrade

And if needed do a reboot

sudo reboot

Install the KDE desktop

sudo apt install kubuntu-desktop

Log out, select Plasma and log back in.

https://computingforgeeks.com/how-to-install-kde-plasma-desktop-on-linux-mint-19/

Allow KDE Connect through firewall

Firewalld

sudo firewall-cmd --zone=public --permanent --add-port=1714-1764/tcp
sudo firewall-cmd --zone=public --permanent --add-port=1714-1764/udp
sudo systemctl restart firewalld.service

UFW firewall

sudo ufw allow 1714:1764/udp
sudo ufw allow 1714:1764/tcp
sudo ufw reload

More information https://community.kde.org/KDEConnect

How to force DPI settings in KDE

To force the fonts DPI do the following.

Open up “System Settings” and under “Font” Select “Force fonts DPI:”  Change the defualt number if needed.

Apply settings and restart the computer.

You might need to do this if KDE is displaying the fonts larger than they should be, or if the title bars are overly large.