You can install SimpleScreenRecorder using the Maarten Baert PPA. To add the PPA and install SimpleScreenRecorder open a terminal window and copy+paste the following lines:
sudo add-apt-repository ppa:maarten-baert/simplescreenrecorder
sudo apt update && sudo apt install simplescreenrecorder
When the installation is finished you can close the terminal window and to start SimpleScreenRecorder press the SuperKey (the key with the windows logo) and type: simplescreenrecorder