Here is an exemple that download all the playable tracks from your pod that match the solar query to the /tmp/testmusic directory (it has to exists beforehand):

funkwhale tracks ls --ids --limit=100000000 --filter="playable=true&q=solar" | xargs funkwhale tracks download -i 500 --overwrite -d /tmp/testmusic

you can omit the --overwrite flag if you don't want the command to overwrite files with the same name on disk (in which case it will exit and raise an error when such a case happens to avoid erasing some of your files)
The first part of the command grabs the ids, the second part of the commnd downloads the corresponding tracks

To be used with the funkwhale CLI: https://docs.funkwhale.audio/cli/index.html

From the funkwhale-troubleshooting Matrix room: #funkwhale-troubleshooting:matrix.org