Style Has Gone Missing!

Hi there, in editor – styles – Onyx styles is no longer there for me. I have checked the .json files and all looks to be in order, it is the styles section on the editor screen where the Onyx option has disappeared. I did switch to a different sytle to test something and I could not find the option to swtich it back, luckily I was still in editor and was able to undo what I had done, else I would have had a nightmare setting the styles back manually.

Please can someone assist with this, as it is causing me problems with the rest of my website build and I don’t want to be updating sytles manually to try and match the Onyx style.

Please note I am up to date with the latest version of WordPress 6.7.1.

See the screenshot below, as you can see Onyx is not there.