I'm experimenting with a 2014 macbook pro upgraded to macOS 14.4 (Sonoma) with OpenCore Legacy Patcher, Linux Mint 21.3 Virginia and Linux Mint 21.3 Xfce.
First, I installed Linux Mint 21.3 Virginia and I could boot both to macOS and Mint. Then, I created another partition and installed Mint Xfce on it.
Now, I can only access both linux operative systems and macOS has disappeared.
What I don't understand is why now the notebook boots directly to grub instead of booting to OpenCore Legacy Patcher
Probably when you installed the second linux you overwrote the boot loader instead of adding a new UEFI entry point.
But I've never had a Mac, so take this with a pinch of salt, and honestly considering things can change based on what, in which order, and how you installed things.. it could be something else.