TL;DR: The character was a mixture of both - a puppet enhanced in post with CGI.
Lighting company Digital Sputnik, which specializes in practical lighting effects used on movie productions, commented on a recent tweet that they have now illuminated both Jesus
Given that the company is fairly new, we can safely eliminate any of the older productions in which he appeared. This, along with a few other hints here & there, would seem to indicate that the character is indeed a practical puppet on-set.
In addition, Star Wars theorist Mike Zeroh claims to have heard from a source at Pinewood Studios that a special set was constructed to accomodate
the Yoda puppet speaking with Luke.
Update: Director Rian Johnson has now confirmed this during an interview with Uproxx...
Neal Scanlan and his team did a recreation of the Yoda puppet. It’s not only a puppet, it’s an exact replica of the Empire puppet. They found the original molds for it. They found the woman that painted the original eyes for Yoda. Then Frank came and worked with them for a few weeks to get the puppet right. He did a lot of testing and a lot of adjusting with the puppet creators. It was amazing to watch the process.
So the answer to your question would appear to be... a mixture of both.