I haved tested today 8th Sept 2022 and found that 'Supplier display name' is the unique field that QBO uses.

Unfortuately you cannot import 'Supplier display name' nor can you set a value such as

• Supplier display name = Company name
• Supplier display name = First name Last name
• Supplier display name = Last name, First name
• Supplier display name= Title First name Middle name Last name Suffix

in the import file which would be good and should not be too difficult for developers to do.

At the moment you need to import your suppliers making sure that no 2 suppliers happen to have the same contact name, since the importing wizard counts the contact name as the unique field rather than the company name. Then after importing you need to painstakingly go through each and every imported supplier and change the Supplier display name to show the company name.

I have found that you can import with blank fields but Contact Name field cannot be blank - however if your spreadsheet/csv file only has Company name you can set Contact Name & Company Name to equal Company Name in the import wizard.