The only reliable way to work with and possibly export old .fp5 databases and save them as .csv files would be to use the very software they were created in - FileMaker Pro. Seems the support for older FileMaker format is pretty limited, so this may not only be your best, but also possibly the only way to convert FP5 to CSV.
Convert FileMaker Pro database file to Comma Separated Value.
We have found 2 software records in our database eligible for .fp5 to .csv file format conversion.
Microsoft Windows software - convert fp5 to csv on Windows
FileMaker Pro for Windows is easy-to-use database software used to create and manage information databases.
Convert from fp5 file
to csv file
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 fp5 to csv. 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 fp5 to csv on OS X
File Maker Pro for Mac is easy-to-use database tool used in business, government, and education to manage their information in databases.