Why doesn't it work?
Elementary OS dropped support for GtkStatusIcon and Ayatana [source] (the two tray APIs most applications use). The reason is probably that they wanted to force developers to make their indicator apps eOS-specific, so that they don't ruin the user experience. For this reason, no old indicator app will work with Juno.
elementary OS Juno is based on Ubuntu 18.04 LTS. Any system update to core Ubuntu will have affect on elementary OS too. It means when Ubuntu 18.04 has been patched with latest sudo, it will be on elementary OS too. You need update your system then to get the new patch.
From your shared link, It's telling:
The problem can be corrected by updating your ...
I recommend using CUPS to install the printer:
Visit http://localhost:631/admin/ in Firefox (it will NOT work in Chrome -> see cannot configure CUPS on elementary OS juno
Click on Add Printer
Login with your elementary OS user and password
Choose your printer's connection protocol
Type your printer's path in the Connection filed
Click on ...
To really launch Flameshot after successful installation:
Go to Applications menu > Graphics tab.
Locate Take Graphical Screenshot flameshot icon.
Right-click it and click Add to Dock menu item.
Right-click this icon in the Dock and click Keep in Dock menu item.
To launch Flameshot, use this icon. (You can delete 'Launch Flameshot' icon from the Dock.)
1) first remove previously added repository:
sudo add-apt-repository --remove ppa:philip.scott/elementary-tweaks/ppa
2) Then add it manually:
right-click Files icon, select New Window as Admin and go to /etc/apt/sources.list.d/;
in that directory, create an empty file and name it philip_scott-ubuntu-elementary-tweaks-bionic.list;
open that file ...