FAQ

Netflix announced a second season. "Volume 2" has been announced to be available May 14, 2021.

I believe they mapped real actors to CGI using a "Head Mounted Performance Capture System" . A quick Google of the term should give some examples.

See 'Trivia' item concerning episode order.

From the trivia section of "Jibaro"

"Due to the hyper realistic movements of all the characters, the textures of water, blood, and the behavior of light, and a multitude of other factors, it almost looks like "Jibaro" is partly live-action, or possibly a mix of animation and motion capture, but the animation was actually done the old fashioned way, using keyframe animation and matching other reference materials to bring the animated short to life. Obviously the CGI used to generate liquid effects and other aspects is all done using high-end modern technology, but in an interview with Screen Rant, Alberto Mielgo said he and his crew actually brought in a choreographer to design the siren's dance and used footage of that performance to match the animated character's motions."

tl;dr: Everything was CGI.