Why multiple efi system for dual boot

I’m trying to install Leap 15.2 dual-booting with Windows 10 retaining secure boot. I expect the installation to add to the existing efi system partition (100 MB FAT) but the installer only wants to create a new 500 MB efi system partition. What’s going on? I couldn’t find a detailed explanation that involves a layout like that.

By default openSUSE installer in Leap 15.2 considers 100M too small. You can always override this in expert partitioner.

It is possible to use the existing EFI partition. But, to do that, you have to use the expert partitioner. Incidentally, this should change in Leap 15.3, which should just go ahead with using the existing partition.

The installer for Leap 15.2 is insisting that the EFI partition should be at least 256M in size. If your existing EFI partition meets that requirement, you would not have this problem. But if your existing EFI partition is smaller, the installer wants to set up a new partition.

If you know what you are doing with partitioning, then you can go to the expert partitioner. Choose the option to use existing partitions (instead of the proposal). Configure your existing EFI partition to be mounted at “/boot/efi”. Create the other partitions as you want them. The installer will complain that you don’t have an EFI partition bigger than 256M, but you can ignore that complaint and continue with the install.

If you are not familiar with doing your own partitioning, then it will be easier to just go with what the installer proposes. It will use a new EFI partition, and that actually works so should not cause problems.

Thanks for the assurances. I’ve used the expert partitioner for traditional (DOS!) partitions for ages, but not on efi secure boot.
I gather I will be fine if I select the existing partition as /boot/efi, and do not format it.

I personally would keep one EFI partition for Windows and one for linux because sometimes Windows update or repair wipes out the boot.efi for linux and for tumbleweed users I’ve been warned that rarely Tumbleweed update can do similar for Windows EFI.

Yes, exactly that.