@jpz4085 Thanks for the clarifications!
@c-o-pr
I don't understand your concern about naming conflicts in multiple boot environments. As long as the bootloaders for each OS are each in their own directory in the EFI partition like:
/EFI/Windows
/EFI/Manjaro
/EFI/OC
I have no problem with this.
Mac uses EFI as staging area for some functions like firmware updates, but I've never seen a conflict.
In modern GPT layouts, put parts any way you want. But keep in mind that there are histories for layouts where that wasn't true, but GPT was around then. This history is why GPT has a fake MBR area, which it IDs in a special way to keep legacy layout tools from blasting it.
To repeat Ubuntu installer has a naming conflict with OC and it replaces a loader file (Bootx64.efi). Note the name suggests a history if x86 (32-bit) vs x64, which has naming.
I'm sure my previous comments can be read in various ways. The subject is too complex to catalog. What I wanted to convey is that what constitutes a viable layout depends on what OS (history) you look at it from, and the corresponding starting point of loading.
Re APFS being just another filesystem type, I didn't want to imply otherwise.
As you have found Apple installer will mess with your layout re EFI min size. Windows installer will probably mess with your layout too. Ubuntu installer is kind-hearted enough to give you "Do something else" option to arrange a suitable layout without messing up existing Win or Mac, but then it goes ahead and stomps on NVMe ESP:/EFI/BOOT/BOOTx64.efi anyway, even if you tell it to install on another drive!
As to other Linux I can't say, but there are so many who has cataloged them all?
The history of this thread is your asking good questions about what happens with OC, whether your layout can work, surprise that Disk Utility munges your EFI, etc, with others pitching by telling to just follow the straight and narrow re OC. It seems you're more comfortable now. My attempt to help was only to expand the dialog a little re straight-and-narrow while advising you that there's no overseer of boot policy except you, and that history informs how various OS take liberties. AFAIK, OC should not be regarded as one loader to rule them all, but maybe they're working on it? IDK
Cheers