Where could I get buildbot .config file? I could keep the same configuration as the buildbot..
You can modified .config with make menuconfig
There is no special config in buildbot, just the current defaults plus a few options targeting buildbot, e.g. build also the "Imagebuilder" binaries etc.
You get the same router options if you delete your .config and then select your device.
But since a few weeks there is a new "config.seed" file in the download directory (same as the firmware images). That is the output of ./scripts/diffconfig.sh (In practice that is the difference between global empty defaults and your device.) You can download it, save it as .config and then run either "make defconfig" or "make menuconfig" to expand it to normal full .config But that is not really sensible as it e.g. enables the Imagebuilder build etc.
For example, for ar71xx devices:
But you can download it and see that there is practically nothing special.
Thank you @hnyman.
Your explanation is very helpful.