Connecting the Amiga directly to the wifi is no-go since the wifi is set up with 802.1x authentication, something the Amiga supplicants never supported. Considering the error message when trying to connect via the mac, it seems that policy is set to not allow "tethering" wired devices behind an authenticated device. Depending on where this policy is implemented it may or may not be possible to use a wifi/ethernet "bridge" capable of 802.1x authentication.
This is what you see as the "enterprise" alternative to "pre shared key" (PSK) in the wifi setup, hardly anyone use it with home access points, but it’s used extensively in more professional environments.