It seems that in the latest KNIME 5.9 Preview (nightly build) the Parquet Reader nodes simply disappear and are not present when opening a workflow featuring them. Also they are not being prompted to be installed.
Try to load this workflow and see the parquet reader not being there on the left side:
Maybe I have to install all of the nightly build again since there seem to be some preview KNIME 5.10 items still in play.
@wiswedel A fresh installation immediately prompts me to install some of this extensions:
a complete re-installation of the nightly build macOS Silicon (KNIME 5.10.0_2025-11-26_10-47-49) and doing the updates and only using the pre-defined installation sites (some are de-activated and seem to require login permissions). The Parquet readers are back 
I am aware this is a nightly build. Just trying to collect more experiences.
Hello Markus,
it’s the same root problem as reported in the other post. The nightly build you are using is no longer a preview of 5.9 but 5.10 and is directly extracted from our master branch. As indicated in the other discussion, we need to improve on two fronts:
master, make version bumps to 5.10 quicker so that we do not confuse our community (=you).Meanwhile, the latter has been completed (note the 5.10 in the installation wizard) but the preview links are something for next time.
As for the problems: We are on it! It’s known – one of the core changes has broken something with these nodes. Will be fixed asap.
– Bernd