Can I make an UBUNTU USB SSD recognizable from a Mac default bootloader?

I am trying to make an UBUNTU USB SSD on a GPT partition, that must be recognizable by every Mac I will plug it in.

So I have on that stick an EFI partition with the correct boot and ESP flags.
Within this EFI partition I have following contents:
I suppose it should be bootable that way.
But no, the Apple boot loader (Starting with ALT key depressed does not see my stick at all).
Has anyone a clue how to proceed?
Thank you for your help.

What did you use to create the USB stick? balenaEtcher is specifically made to create Mac-bootable flash drives.

Since there is no ALT key on a Mac keyboard, I'm assuming you mean the "option" key? It also depends on whether you are using an Intel-based Mac or Apple silicon. A complete guide to booting a Mac from USB can be found here.


The Mate install stick was created from Balena, but then I have installed a fresh Mate system on a second USB disk, including boot partition and boot loader.
But that one is not recognized.

My Apple A-1243 german keyboard has indeed an "alt" printed on the option key.
And a Guide how to boot macOS from USB is not useful.
I need a guide how to boot Ubuntu from USB on an EFI-Intel-Mac.
IMHO Ubuntu Mate will not perform very well on an Apple Silicon Mac.