FileMaker Pro supports both the import and export of Excel formats and thus it should be quite possible to export databases from FileMaker as Excel spreadsheets. It doesn't seem that any 3rd party programs support older FileMaker databases so there probably are no other choices for FP3 to XLSX conversion available.
Convert FileMaker Pro database to Microsoft Excel Open XML workbook and spreadsheet.
We found 2 software records in the database related to .fp3 to .xlsx file format conversion.
Microsoft Windows software - convert fp3 to xlsx on Windows
A program used to create and manage information databases
Convert from fp3 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 fp3 to xlsx. 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 fp3 to xlsx on OS X
A database management program for Mac