On Mac OS you can write the image with dd in a Terminal. 100% reliable and no extra software needed.1. Insert USB drive, start Disk Utility, select USB drive, Cmd-i for info, memorize disk unit (disk2, disk3, or similar), click on "deactivate" in the tool bar (not "eject"!)...
jakub@Jakubs-MacBook-Air Downloads % diskutil unmountdisk disk4 Unmount of all volumes on disk4 was successfuljakub@Jakubs-MacBook-Air Downloads % bzip2 -dc OPNsense-24.1-vga-amd64.img.bz2 | sudo dd of=/dev/disk4 bs=1m0+123213 records in2283+1 records out2394402816 bytes transferred in 601.180059 secs (3982838 bytes/sec)
Sounds more like an issue with the machine trying to boot from the USB flash drive. Is that in UEFI or legacy BIOS mode? If UEFI, did you disable Secure Boot?CheersMaurice