No, you only need to be logged into iCloud and Game Center with the same account.
Access your Apple Arcade gameplay data on all of your devices - Apple Support
You can use iCloud and Game Center to keep your progress, high scores, and game saves up-to-date across your devices.support.apple.com
Thanks for confirming. Those settings are on by default and I have double checked. Games aren't syncing progress. I can see points I earned in one of the games but it is forcing me to play all the levels again to unlock them.
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Basic cartoon graphics because high end realistic graphics are beyond the development budgets of these kinds of indie titles.
These launch games are not low budget like the much of the app store. A few of them have the credit 'Produced by Apple'. You missed the more obvious thing. The games are iOS ports and not developed for anything else but mobile GPUs. I found a few games have extra settings on the macOS version that allow higher resolution but not extra detail.