Install Open Broadcast Software (OBS):
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For Ubuntu 15.04 and newer:

First must have ffmpge
sudo apt-get install ffmpeg

Then add obs repo and install
sudo add-apt-repository ppa:obsproject/obs-studio
sudo apt-get install obs-studio

https://github.com/obsproject/obs-studio/wiki/Install-Instructions#linux
https://obsproject.com/

Origonal Creation date in Vivaldi: 8 November 2018 @ 12;52

Update: July 28th, 2021:
To enable hardware accelleration on intel systems: go to setting to advanced mode and selecting FFMPEG VAAPI. It will never show up as an option in the simple configuration mode.
source: https://obsproject.com/forum/threads/hardware-encoding-not-available-ubuntu-19-10-w-nvidia.113789/