Cannot create Debian bootable USB from a Mac

Hey All,
I’d like to reinstall Debian on an old MacBook (intel core i5, so i386) from an existing and more recent Mac (M2).
I’ve downloaded the i386 netinst (« little cd »)
tried the methods described on both Debian and Ubuntu pages (links below). The operation completes successfully, but the USB key isn’t identified as bootable: When starting the system with « Alt », all I can select is the usual internal disk.
Is there another way to verify the validity of my method, or another way I can try to create a bootable USB?

Do I need to convert the ISO with hdiutil or is it ready, and a cp is sufficient?

If I do a simple cp, is the old FAT file format sufficient?

Many thanks!

Resources used:

• https://www.debian.org/CD/faq/#record-mac
• https://help.ubuntu.com/community/How%20to%20install%20Ubuntu%20on%20MacBook%20using%20USB%20Stick
• https://ubuntu.com/tutorials/create-a-usb-stick-on-macos#5-etcher-configuration

Tools used:

• dd
• hdiutil and then dd
• etcher