Plenty of accounting and tax preparation programs support formats from Quicken, so it may be well possible to convert .qfx files to .qif files using some of them. Of course you can also use Quicken itself to convert qfx to qif files.
Convert Quicken Financial Exchange format to Quicken Interchange format.
We have found 5 software records in our database eligible for .qfx to .qif file format conversion.
Microsoft Windows software - convert qfx to qif on Windows
A personal finance management program by Intuit
Convert from qfx file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned qfx to qif. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert qfx to qif on OS X
Mac version of popular Quicken personal finance management software
A personal finance organization and analysis tools
An accounting software for Mac
Multiplatform software - convert qfx to qif on any platform
A personal finance manager