Why does LT spice limits frequency domain output to 65535 data points?
Break the desired frequency range into smaller ranges, each with 65535 points, and run a separate simulation for each range. Concatenate the data from the simulations and plot it using some other tool.

By the way, you will not get 100% accuracy...ever. If you state that as your goal then it makes it very difficult to achieve what you really need in a reasonable amount of time. I doubt very much that you really need 100 million data points.