Quicken for Mac 2018+ imports QFX files, QIF files, and CSV Mint files (QIF and CSV Mint files are importable into a new account, but easily moved to another account) Which file formats does Quicken for Mac import? QIF files have to be created correctly to be imported. Quicken for 2017 or earlier for Windows imports QIF files only.
Quicken for 2018+ for Windows imports QFX, QIF files, and QIF files are 'officially' supported by Quicken. Which file formats does Quicken for Windows import? The same applies to QFX and CSV Mint files. In case your Quicken imports QIF and QFX files, either format has issues and advantages. See below which format your Quicken imports and choose a converter to convert your files to a Quicken importable format.
To Quicken: Convert transactions to an importable by Quicken format