I would recommend using an application called PabloDraw by Picoe Software. The installation is quite straight forward, as long as you install all the dependancies:

First you need to add the repo for mono 2.10

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
echo "deb https://download.mono-project.com/repo/ubuntu stable-bionic main" | sudo tee /etc/apt/sources.list.d/mono-official-stable.list
sudo apt update

Next you need to install mono-complete and gtk-sharp2

sudo apt install mono-complete gtk-sharp2

Now once this is installed, download the linux .zip file from Picoe

wget http://download.picoe.ca/pablodraw/3.2/PabloDraw-3.2.1.zip
unzip PablowDraw-3.2.1.zip

Finally, and this isn’t documented as far as I can see, PabloDraw only seems to see files that are lowercase in folders, so rename all the files you want to use to lowercase. An easy way to do this, is the following in the folder you have the files that might be uppercase;

zip -r foo.zip foo/*
unzip -LL foo.zip

This will install all the necessaries to run PabloDraw with mono 2.10.