Assume I got/downloaded (in the past) a bootable ISO file which contains a software which can later be installed onto a bootable USB flash drive.

How can I detect if this ISO file is for Legacy BIOS or UEFI based computers?

Of cause without trying it out.

Can I somehow peek into the ISO file archive and search for a certain file which is special for one of the two boot types (and not the other)?

Which file is it? Is it the same for 32bit AND 64bit?

As you know ISOs resp. bootable USB flash drives can contain dual boot bootloaders for Legacy BIOS AND UEFI.

How can I find out if the ISO is such a dual-boot ISO?

Thank you