Ventoy does not depend on having booted as UEFI to create the USB – Ventoy does not care – it is only when you wish to use the USB to boot, that is must boot as UEFI.
Question:
Are you booting with the old USB (MBR) – Cruzer Glide 3.0 – and then expecting to write the Ventoy system to that same USB?
- You can’t do that… because the USB is already in use!
It doesn’t matter what application you use to create the USB;
- You cannot create a USB installer if that USB is already being used to boot with.
However…
- You can write to a second USB (that is not being used to boot with).
Do you have another USB?
The Ventoy GUI and CLI work well – both in Linux and Windows – provided that the correct settings/parameters are applied.
A caveat with CLI in Windows, though – some users may be unfamiliar with how PATH works in Windows (the Ventoy app must be added to PATH) and there is no convenient install routine to do that for them (it’s distributed as a portable app in a .zip file).
I imagine this is a rare caveat, though; I mean, the command-line in Windows is rather rudimentary compared to Linux. 
Yes, with Ventoy (or Rufus) it is different.
The boot mode must be explicitly set via the Ventoy app configuration before creating the USB – to force GPT partitioning of the USB – otherwise it defaults to MBR/Legacy.
Because the Manjaro ISO isn’t booted directly, but selected from a list after the USB has booted, the boot mode is inherited from the Ventoy USB.
Thus the importance of changing the (very simple) Ventoy settings before creating the Ventoy USB.
In the case of Rufus similar settings exist; the difference being that (unlike Ventoy) Rufus writes the ISO directly to the USB – Rufus still needs to be “told” which partitioning to perform (GPT/MBR).
However, if (as I suspect) the OP is trying to both boot with the USB and write to it at the same time, they have bigger problems.