I think the package of dump978-fa available from flightawre isn’t working on buster yet.
But i think the dev branch on github works.
If you are using two rtl-sdr dongles you also have to serialize the dongles.
You can use this guide:
Dump978 Add-On Installation Procedures? - #17 by abcd567
Note that you will need the dev branch of dump978
Instead of
git checkout v3.7.1
you need to
git checkout dev
Might still not work.
As you already have dump1090-fa working, no need to install that or download the git for it.
But both dongles need the serial as described there.
You might also need to use rpi-update if you haven’t done so already.
(newer kernel version so rtl-sdr works properly)