My educated guess - no. With your setup, two AX devices, probably negotiate a faster (PHY) connection over WiFi using than GigE. It COULD even be faster (real world, not theoretical) than GigE but I know we love that guaranteed 1ms response time and stability.
IIRC when you set up LAG, it adds another interface (ifconfig to list them) and since Ethernet backhaul uses eth0 (Wan port) and the AI Mesh code is probably very inflexible, I doubt ASUS would ever put the effort into moving the backhaul 'port' from wan to the LAG ports.
Best recommendation -'upgrade' (I know - rt-ax88u are already old) to one with 2.5GigE WAN ports. RT-AX86U - newer but 'less' than the RT-AX88U.