MacBook Pro cannot detect bootable USB on boot menu

Hello emir228,

After reviewing your post, it seems like you do not see the USB drive as a startup disk on the MacBook Pro, but you did on an iMac. We would recommend you use this article to help troubleshoot the issue.

"If you're in Startup Manager and can't see a third-party startup disk, the startup disk could be using Option ROM firmware. To enhance system security, Mac computers with up-to-date software don’t show devices that use Option ROM firmware until you load their firmware. To do that, press Option-Shift-Command-Period while in Startup Manager. If your startup disk appears, do that each time you want to start up from it or from another disk connected to it."

How to select a different startup disk

Please don't hesitate to let us know if the steps resolved your issue or if you need additional assistance.

Thank you for using Apple Support Communities. Have a nice day.

Some Macs just won't recognize the Linux boot loaders with Startup Disk System Preference. See if Option Booting allows you to see the Ubuntu USB drive.

FYI, while Ubuntu may boot this Mac don't expect most of the hardware to be functional unless you custom compile the kernel with some out of tree kernel patches to support the new style keyboard & trackpad (unless Ubuntu has already done this for you). WiFi drivers don't really work unless you have the non-Touchbar model due to firmware issues with the Broadcom WiFi chips which Broadcom is not going to fix for the Linux users.