Your new BE96U is quite an upgrade from your AC3100. I own both of these. The BE96U has greater range, a 6GHz band, greater throughput, as well as increased security and more features. Used alone, it should offer much improvement and your AC3100 can be added in mesh. However, I advise not adding the AC3100 as it will create conflicts and lower throughput.
The answer to your question is yes and no.
First, be sure to do a WPS Factory Reset when you update the firmware. This is imperative.
You will need to create a combined IoT SSID for 2.4GHz and 5GHz bands as this will insure legacy device connection. I advise to not combine the 5GHz band with the 6GHz band SSID or you will risk a conflict with the current BE96U firmware. This will give you a WiFi 7 2.4GHz SSID, a WiFi 6 2.4GHz and 5GHz SSID, and a WiFi 7 6GHz band SSID. DO NOT TRY TO IMPORT YOUR AC3100 SETTINGS WITH SOFTWARE. You will need to input your AC3100 SSID and Security Password manually. (The BE96U may also require a stronger password.) This will allow most client devices to connect within about 30 minutes - if you didn't have to change your password. SOME client devices may still need to be added again manually for connection. DO NOt TURN ON MLO.
Using the BE96U, you should experience your full Internet connection capacity. You should see Wireless transfers rated as high as 5Gbps to 9Gbps. Enjoy your new router.
