A WPA3 network disallows outdated legacy protocols and requires Protected Management Frames. Gear certified before July 2020 is where that bites. Check the transition mode and your band names first.
Wi-Fi 7 beats 6E for exactly two reasons: channel width doubles to 320MHz and each subcarrier carries 12 bits instead of 10. Multiply and you get 2.4x. But 4K QAM needs roughly 42dB SNR, so it only switches on close to the router.
The dividing line across the three generations is the 6GHz band. Wi-Fi 6 uses 2.4/5GHz, 6E adds 6GHz, and 7 layers on 320MHz, 4K-QAM and MLO for a theoretical 46Gbps. Here is where the speed actually comes from.