To verify if a removable media (e.g. USB, DVD, or ISO) is bootable, you could use file tool on Linux systems. The command
file -s /path/to/media reads block special files, such as partitions, and outputs the information.
To test this, I inserted RHEL 8.2 Installation ISO as a disk in a VM. The device path is
/dev/sr0. Once I verified the disk is accessible, I ran
file -s /dev/sr0. The output for RHEL Installation ISO shows the disk as a DOS / Master Boot Record partition, meaning it is a bootable media. For the second test, I used a Windows 10 Installation ISO. The output shows the media is a CD-ROM filesystem that is bootable.
An observation: Notice the Windows media output states the media is bootable, unlike the Linux media, that only shows partition information.