You do seem to be off on the wrong track.
By booting from a gparted live ISO you would boot into an environment where your normal drives and partitions are not mounted, so you will be free to manipulate them.
That said, to increase the EFI partition, you will probably have to also use gparted to reduce the size of whatever is adjacent to it. So you have to be happy to do that. Gparted can adjust the size of partitions without data loss, so this is feasible/doable.
In my own case I booted into an alternative OS, which is pretty much the same as using a live ISO. I then reduced the size of the partition adjacent to boot EFI, then I enlanged the EFI partition. This all went quite smoothly, but you have to be sure of what you are doing.
If you’re not confident in doing this kind of fiddling and haven’t really done much beyond installing your OS, then it may well be easier to just reinstall and manually setup a new partitioning scheme.
If you’re not so interested in systemd-boot or grub-bls, it may be easier to switch to using grub2 which doesn’t use as much space as systemd-boot or grub-bls. But you might like to request someone provide a precise series of steps. I can’t help with that, I haven’t tried switching boot loaders recently.
I would add, because OpenSUSE is going through some changes to boot loader, the installer hasn’t caught up, and some unexpected issues are also causing changes in direction. Unfortunately things are a bit bleeding edge at the moment, installation is not normally this painful.