Question about Digitus HDMI eARC converter/splitter

No, unfortunately not!

This converter does exactly the opposite: it converts an ARC or eARC signal into a normal HDMI signal for older AV receivers WITHOUT ARC functionality.

If I understand you correctly, you want to transfer an audio/video signal from your PC to the soundbar? You don't need an eARC adapter for this. ARC stands for "Audio Return Channel", which means that the picture comes from the TV and the sound is sent back to the soundbar via the same cable, as the TV does not have a separate HDMI output.
Unfortunately, I can't say exactly how this works with Dolby Atmos on the PC - except that it works with Dolby Access.
I hope I was able to help you.