Thank you for posting this case in Microsoft Community!
Based your description: No spellcheck in new outlook Editor greyed out. I would like to cooperate with you working on this case. To clarify this case, it is suggested that you need to follow below workaround:
- Firstly, please try to sign in Outlook Web via Microsoft Edge and check if Editorfeature is working fine or not.
2. If also greyed out, please clear browser cache: for Microsoft Edge see How to Clear Your Cache - Microsoft 365.
- If still not working, please follow these steps. In Microsoft Edge: Click on the three dots on the upper right corner > Extensions > Get extensions for Microsoft Edge > in search bar type Microsoft editor > get. After installing the editor extension, you may check if Editor function available in Outlook on the web.

- Then you can go back New Outlook and reopen the app to check if working fine or not. If still greyed out, please also go to Outlook on the web and perform following steps:
- Using the menu list, select Editor > Editor Settings.

- The Microsoft Editor Settings panel is displayed. Select the buttons on or off per your preferences. If needed, you can select Reset to default.
- Select OK to return to your draft.
By the way, if above all steps still not resolved your case in New Outlook, please follow below rest steps further:
- Please make sure if your New Outlook has been upgraded to the latest version.
- You may perform the further steps as shared Microsoft article Troubleshooting Outlook for Windows issues.
If this case still persists, please also contact New Outlook for Windows Support Team via clicking Help>Contact Supportor Contact support and provide feedback within the new Outlook for Windows. The support team over there has higher permission than us, they can remotely help you and collect logs at your convenience. They can also involve more resources to investigate the issue from backend side. This would be the most efficient way in handling this case for you.
If you need further assistance, please feel free to let me know, I will keep assisting you.
Your understanding and patience will be appreciated.
Thank you!