The best way to install Inkscape is by using the Ubuntu Sotware Center.
Simply open Software Center and search on Flameshot.
Click on Flameshot and follow the install Process
You can also install Flameshot via Terminal.
Open terminal either by pressing Ctrl+Alt+T on the keyboard or by searching for ‘terminal’ from the system application menu. When it opens, run the commands below:
sudo apt install flameshot