3060, USB flash shows in UEFI; sometimes, it doesn't

Neither Rufus nor Linux is supported here.

Newer models don't support every distro every version on the planet.

Current Ubuntu is 18.04 LTS

There is support for Redhat and Suse and Ubuntu but it is not free.

You should try a Legacy boot USB with Casper persistence file.

https://www.pendrivelinux.com/universal-usb-installer-easy-as-1-2-3/

 

I'm also pretty sure that legacy wont boot on a 3060 on anything other than USB flash drive aka you can't legacy boot internal hard drives regardless of OS.

https://www.ubuntu.com/download/desktop/thank-you?country=US&version=18.04.1&architecture=amd64

 

 

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I also faced this problem when installing Win10 using a USB flashdisk on early Oct 2018. The root cause is that there is a BIOS bug on Dell Optiplex 3060 that prevents you booting from USB drive with correct UEFI info and right settings in BIOS. Dell already announced the fix of this bug on the BIOS update at end of Sept 2018. After flash the BIOS at that time, the problem disappears. I forget the exact BIOS version number that resolved this problem, because Dell don't provide full version history of their BIOS in the website. The history version link for BIOS only provides some selected version which don't include the end of Sept 2018 version I flashed.