wan mtu

Hi guys, I bought an Asus RT-BE88U, I really like this router, and I was wondering if the new BE routers from Asus can do MTU 1508 over PPPOE with baby jumbo frames? My ISP is Telus, but last mile carrier is Bell and they are using PPPOE with VLAN 40. So I was wondering if I could achieve that...

I know that VPN MTU and WAN MTU settings are interface specific—but I’m looking to understand, is the actual optimal VPN MTU limited by the optimal WAN MTU? I think my optimal VPN MTU is higher than my optimal WAN MTU. (How) is that possible? Why wouldn’t my optimal VPN MTU, in practice...

If I change the WAN MTU will it apply to my OVPN client configurations too, or do I need to change the MTU in individual custom configs in the OVPN client settings also? thank you