As per https://www.raspberrypi.org/forums/viewtopic.php?f=78&t=195612&p=1699352#p1699389, the downloader not downloading ARM binaries is indeed a problem. At a minimum, the script should have the Arm/Arm64 binaries added, though honestly it'd probably be better to just build STK without the recorder and avoid this whole mess.
As per https://www.raspberrypi.org/forums/viewtopic.php?f=78&t=195612&p=1699352#p1699389, the downloader not downloading ARM binaries is indeed a problem. At a minimum, the script should have the Arm/Arm64 binaries added, though honestly it'd probably be better to just build STK without the recorder and avoid this whole mess.