What is the maximum cleaned traffic (bandwidth) can be forwarded from F5 i10800 AFM to customer via GRE tunnel?

Your question is confusing, but here is the information I think that may help you.

Based on the datasheet, i10800 can handle:

Throughput: 160 Gbps/80 Gbps L4/L7

https://www.f5.com/pdf/products/big-ip-platforms-datasheet.pdf

With Silverline, you are charged per clean traffic, but I haven't seen any information that says 1G is the maximum, as that does not make sense.

Here is the datasheet about that:

https://www.f5.com/pdf/products/silverline-ddos-datasheet.pdf