Because they have packaged MacOS and Win version in the same zip file in the past - really with Unity, most of the files remain the same except for a few os-dependent files. This is not unusual for developers to do.
8GB RAM should be enough to run this. Though, if you have an SSD, Windows11 and an i7 --- you really should have 16GB RAM at the minimum (yes, I know that Win11 should run with 4GB RAM with little problem and they say 8GB RAM is adequate... but 16GB to 32GB really should be a person's goal with Win11).
Perhaps there was an error in your download or something did not extract properly. You could try downloading and extracting again. I have no problem running this on my Win11, i7, SSD machine... Heck, I'm even running it from an SSD external drive.
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