Hello,
I use LMDE6 and am looking for a tool like SmartSniff for Windows. Unfortunately I have not found anything.
Does anyone have tips?
You can try Wireshark, but not the Flathub version
Too bad there’s no such tool for Linux. 
Actually, I didn’t want to use Wireshark because it is too extensive for my purposes.
Why not the Flathub version? Which one do you recommend?
Too bad there’s no such tool for Linux.
Wireshark is the only graphical tool that I know, but I’m not that deep into network sniffing, so there may be a hidden gem that fits your needs. Mist of the tools I heard of are command line programs.
Why not the Flathub version?
Due to limitations of the Flatpak Sandbox, Wireshark is not able to capture traffic.
Which one do you recommend?
Install it from the Repos of your Distro.