Choosing a 64GB MacBook Pro 16-inch results in a lead time of 8-9 weeks.
DRAM suppliers are generally carrying a healthy level of inventory, so there's no reason for this level of delay. In fact, PC DRAM prices are expected to decline for Q4 due to ramp down of WFH and remote learning.
Right now, other BTO configurations only have a 3-4 week lead time. I expect those dates to become late November as we get closer to launch.
We saw this situation back in 2019 and I posted a thread about it here. (The 16-inch model launched Nov. 13, 2019.)