Which soundbar?

The PLAYBAR, the PLAYBASE, the first generation of the Beam, and the Ray, no.

The second generation of the Beam, and the Arc, yes. 

You to be sure: what do you mean by "compatible”. Because eARC is backwards compatible with HDMI-ARC, an eARC capable speaker will work on HDMI-ARC. ARC-capable speakers will work on eARC. So the (HDMI-ARC) Beam Gen 1 will work with an eARC TV, you will just not get Atmos. Playbar, Playbase and Ray al optical only, sou will not work with eARC, but with the optical connection taht is on allmost all TV's..

It is the first ever Playbar Sonos introduced about 9 or 10 years ago. 

Thank you for your response!

eARC did not exist as a standard 9 or 10 years ago. Even ARC was pretty new back then.