I'm on Xubuntu 64 bit. Unetootin isn't detecting my USB. Startup USB creator doesn't work on all the ISOs. I want a bootable USB creator, that works on ubuntu 64 bit. It has to be updated and has a nice GUI and free.
You can also use
dd which is included by default in most distributions, however it's not GUI-based.
Example usage :
dd if=/path/to/your/image.iso of=/dev/sdX
This won't show any progress though, the command will end once the process is complete.
/dev/sdX with the actual path to your USB drive - note that this will copy the entire ISO filesystem to the drive, so it'll actually behave more like an USB CD drive rather than a flash drive and some BIOSes may not like that and won't boot from it (but personally I never had such an issue).
After trying a few, I settled on Ventoy.
You can select which .ISO you wish to boot from - just add and remove the .ISO files as you wish :)