From my experience with a previous installation of Fedora on an old MacBook alongside macOS (and windows), I think this is rather Fedora reinstall issue than a Mac issue.
If I understand well, you did keep the macOS installation and it is functional (recommended for firmware updates). If yes, then it is normal to have two start-up stages:
- the first one is mac’s Startup Manager, which lets you select from the available startup disks or volumes
- once you select Fedora, the second one comes in, and the boot process of the Fedora installation will be kicked off.
At this point, it is normal for grub to take over the boot process, be it with or without displaying the boot menu. So I would say you need to fix grub, which might have been affected in case you’ve reinstalled Fedora without erasing the older Fedora partitions and therefore without letting the new install recreate new, clean /boot and /boot/efi partitions.