Hi!
Thank you for posting your query on community forum!
As I understand the spell checker in excel is not working, make sure to enable spell check in you excel here I am sharing you the steps for:
Enable Spell Check: Ensure that spell check is enabled. Go to the "File" tab, select "Options," then click on "Proofing." Make sure the "Check spelling as you type" option is checked.
The following support article has more information regarding the sell check in Excel:
Check spelling in a worksheet - Microsoft Support
I hope this resolves your issue, but if you need further assistance feel free to reply.
Best regards,
Scott | Microsoft Community Moderator.