Hello there Sitt,
You seem to have figured it out all by yourself, but I will try to explain why you couldn’t install OpenSUSE on the microSD card: you already had an image on it and you booted from it and entered the installer. The way I see it, it is not possible to install an OS on the same media from where you booted the installer.
Unfortunately Le Potato does not support boot from USB (at least I am not aware of this capability…someone who knows better please correct me!), which would allow you to boot the installer from USB and install on an microSD card, for example.
The only way this would work is in the case when you have also an eMMC module attached to the board. That way you can boot from microSD card and install on the eMMC module. That is how I personally do it: I have a microSD card with Debian 12 with Gnome Desktop Environment and, while I am booted from this medium, I download images and flash them on the eMMC module. Once that is done, I power down the board, remove the microSD card and boot from the eMMC module. In here Libre Computer recommended eMMC image flashing you will find the method that I use, plus another method, if you do not like this one.
My questions to you is: why do you need OpenSUSE? You have a specific usecase for it or need certain software like YAST?
For any server needs on the Potato I use Armbian and DietPi, or you can use the Official images posted on this forum, here Official Supported Images.