Hello @FreddyMasterLao
I'll try to answer these questions as best I can.
1. Regarding WPA3, WiFi 6E requires WPA3, so it is always enabled for clients connecting to that band (including the hidden mesh interconnect between units – 6GHz is always used for the mesh interconnect on Nest WiFi Pro). The setting to enable or disable it on Nest WiFi Pro applies to the other two bands (2.4GHz and 5GHz). Where this comes into play is that some clients that support 6GHz (WiFi 6E) have trouble handing off between the different bands if WPA3 is not enabled for those other bands. However, unfortunately, some other clients that do not support 6GHz have trouble if WPA3 is enabled on 2.4GHz and 5GHz. So, it has to be configurable. I would enable it and make sure all your devices still connect properly to the lower bands.
2. Regarding performance, this is complicated. Mesh networks trade performance for increased coverage area. But, predicting what the performance will actually be depends on so many factors, it would be an oversimplification to say "drop in half". For example, if a client is connected to a mesh secondary via 5GHz, that traffic will be getting sent to the primary via 6GHz. You may not see much performance degradation at all (assuming the secondary is close enough to the primary). But, if the client is connected to the secondary via 6GHz, then the traffic has to go over that channel twice, reducing the end-to-end performance. But! Since the 6GHz band supports wider bandwidth (unless you have wide channels enabled for the 5GHz band?), the result may still be comparable. Like I said, it's complicated and hard to predict.
3. Regarding clients connecting via WiFi 6E (6GHz), yes – potentially. See the discussion in the answer to question number two. Again, mesh networks expand useful coverage area. Also, 6GHz is currently still limited to lower transmit power, which limits the interconnect speed at longer ranges.
I would just close by saying if you really want the absolute highest performance possible, connect the Nest WiFi Pro secondary/point units back to the Nest WiFi Pro primary/router unit's LAN Ethernet port (through an inexpensive, unmanaged Ethernet switch). That way, all three bands are available on all of the units without having to share any of that capacity for the wireless mesh interconnect. This also lets you place the secondary/point units further away, enabling the maximum performance over the maximum coverage area.
I hope this helps!
