How to save a bootable USB flash drive image in ISO?

Question

USB

Colleagues, it seems like a simple problem, but I don’t know a simple one-way solution.
In short, the following is given:
There is a motherboard that comes with a BIOS updater. At startup, it asks you to specify a USB flash drive, makes it bootable, you can then boot and update from it.
There is a Zalman 350 pocket that can mount an ISO image. Accordingly, I want to make an ISO from a bootable USB flash drive, which I will feed to Zalman.
I found the "USB Image Tool", but it can only *.img, and Zalman cannot mount such files. Found "IMG to ISO", but it crashes with the message "unable to create vdisk" or something like that.
Of course, I understand that I can contrive to make a bootable CD using files from a flash drive and pull the ISO off it, but it's like cutting tonsils with an autogen. Maybe someone knows an easy way?