Very much appreciate the update to MC v1.16.1, though there appear to be some issues with the new version.

There is an error message about Jankson in the log and extra blocks do not appear to be available in the world.
Tested with EP v2.9.0, MC v1.16.1, and Fabric API v1.16.0 and v1.16.2 in a new MultiMC instance with default settings.
I also tested with a newer Jankson extracted from another mod, but the same issue persisted.

Latest log attached.
latest.log

EP Addon has not been updated to 1.16.1 yet, so that not working is to be expected. Adorn's error is on their end.

Try deleting the default piece pack (found in config/extrapieces/default.json) and see if that helps. Regardless, I will try and fix this soon.

Didn't find it in that exact location, but it's a test instance, so I deleted the entire /config/extra pieces/ and was able to launch, run, and grab/place pieces (didn't test them all).

It does work on it's own now, but fails with EP Addon (v1.0.2) and/or Adorn (v1.9.1).

Also tested in a larger load list and, of the mods I'm using, still only seems to conflict with Adorn and EP Addon.
Looks like there is an open Issue in Adorn's Git (Juuxel/Adorn#92) with a workaround; editing Adorn's jar per the description does seem to get EP and Adorn working together for me.