Opensuse-migration-tool from Leap 15.6 towards Leap 16 and slowroll are ko

OK, so it is indeed too old for Leap 16 (it doesn’t support the minimum x86_64 v2).

zypper should offer some options when such errors arise, if we don’t see the exact name and version of the packages and we cannot see what alternatives are offered we cannot help much.
Try again when you have access to the system involved; usually CTRL+SHIFT+C copies selected text from terminal emulators, then paste here.
If you cannot do that even a photo of the screen with errors is better than telling stories.