Project X-Ray [1] and Project U-Ray [2] are the best source for configuration details that Xilinx/AMD doesn't publish. These projects focus, respectively, on the 7-series and UltraScale FPGAs.

[1]: https://f4pga.readthedocs.io/projects/prjxray/en/latest/

[2]: https://prjuray.readthedocs.io/en/latest/