Technically - the ISO should be used as-is - how exactly that translates into real world depends on how you handle your storage medium.
Grub offers the option to boot the ISO by reading the ISO directly from disk.
- This is the approach used by Ventoy
- A similar approach is described in [HowTo] Boot Manjaro ISO directly with GRUB
The only method that do not work - ever - is the iso-mode originally used by Rufus and claimed as the only way. After contacting Manjaro - the Rufus developer changed how a Manjaro ISO is written to be a byte-to-byte copy - known in Rufus as dd-mode (the actual documentation has been lost to the byte-void).
That means - any software capable of doing a byte-to-byte copy will work.
As Grub - usually - is capable of booting the ISO directly, Ventoy is widely accepted and so is the more manual approach as it has been described in [root tip] [How To] Multi ISO USB with storage partition.
One could say that creating a byte-to-byte copy of a Manjaro ISO, to the chosen target medium should prove without any shred of doubt that the ISO is bootable and fully functional.
I do want to add that one should always use a suitable USB-stick, as using a DVD is discouraged as the loading of the desktop may be unreasonable slow, thereby causing a bad experience.