FileMaker Pro supports export to Excel's formats and as such it is possible to convert FMP12 databases to XLS or even XLSX formats. Support for FileMaker formats is fairly limited, so without the program itself you probably cannot otherwise convert FMP12 to XLS.
Convert FileMaker Pro database file to Microsoft Excel 97 to 2003 workbook.
We found 2 software records in the database related to .fmp12 to .xls file format conversion.
Microsoft Windows software - convert fmp12 to xls on Windows
A program used to create and manage information databases
Convert from fmp12 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 fmp12 to xls. 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 fmp12 to xls on OS X
A database management program for Mac