Has anyone an idea what race this character is?
This is the creation of digital artist Serge Birault. You can find the original version of the artwork on their Art Station profile here (this still loads initially but then redirects to a 404 for me currently). This is what the page looks like, note the title "We have cookies" and the caption "Quick female Sith concept for fun":
The second iteration, the one in question, can be found here. Note it also has the title "We have cookies #2".
Serge also posted this on their Twitter page here with the caption "SW fan arts." showing both version of the art.
It's also worth noting though that Serge is Lead Concept Artist at Virtuos, a company that has had involvement working with Star Wars. For example, they worked on Star Wars Jedi: Fallen Order. It's unlikely this was work created for Fallen Order given the time Serge posted it on their profile but it could have inspired future work. Having played Fallen Order this does strike me as somewhat similar, costume-wise not species/race, to the Second Sister and note she also has a dual lightsaber.
So, whilst not a direct inspiration for the character I can see some similarities between the two.
However, to answer your question it would appear that this is just fan art and so the female character has no known race/species and isn't canonical.