I'm curious about this as well. I often see people talk about CockroachDB in production, but I don't think I've ever heard of anyone running Yugabyte. But it is definitely under active development.
I found two threads discussing it from the past year:
https://news.ycombinator.com/item?id=39430411
https://news.ycombinator.com/item?id=38914764
Yugabyte (as with CockroachDB and TiDB) is based on mapping relations to an LSM-tree-based KV store, where ranges of keys get mapped to different nodes managed through a Raft group. That kind of structure has very different performance characteristics compared to Postgres' page-based MVCC. In particular, LSM trees are not a free lunch.
Query execution is also very different when a table's data is spread over multiple nodes. For example, joins are done on the query executor side by executing remote scans against each participating storage node and then merging the results. That's always going to be slower than a system that already has all the data locally.
YB also lacks some index optimizations. There is some work to make bitmap index scans work in YB, which will give a huge performance boost to many queries, but it's incomplete. YB does have some optimizations (like loose index scans) that Postgres does not have. So it's probably fair to say that YB is probably a lot slower than PG for some things and a little faster at others.
I think it's fundamentally not a bad architecture, just different from Postgres. So even though they took the higher layers from Postgres, there's a whole bunch of rearchitecting needed in order to make the higher layers work with the lower ones. You do get some Postgres stuff for free, but I wonder if the amount of work here is worth it in the end. So much in Postgres makes the assumption of a local page heap.
What we see in cases where someone takes Postgres and replaces the guts (Greenplum, Cloudberry, and of course YDB) is that it becomes a huge effort to keep up with new Postgres versions. YDB is on Postgres 12, which came out in 2019, and is slowly upgrading to 15, which came out 2022. By the time they've upgraded to 15, it will probably be 2-3 versions behind, and the work continues.
Worth noting: Yugabyte was tested by Kyle Kingsbury back in 2019, which uncovered some deficiencies. Not sure what the state is today. The YB team also runs their own Jepsen tests now as part of CI, which is a good sign.