Is "supposably" a word?

AI tells me, "Yes, 'supposably' is a real word listed in major dictionaries like Merriam-Webster and Cambridge Dictionary.  However, it has a different meaning from the much more common word 'supposedly,' even though the two are frequently mixed up in daily speech."  Here are the differences:

• Supposably:  Means conceivably or potentially possible (e.g., We could supposably finish today).
• Supposedly:  Means reportedly or by reputation, often with doubt (e.g., He is supposedly rich).