Typically AGC is used to increase the noise level. If my receiver sensitivity is -100 dBm with 60 gain After AGC it becomes -40 dBm. If the noise figure of AGC is less. So the noise also increased by 60 dB. High bandwidth has higher noise floor? How does it affect after ADC?
All noise that reaches the power detector that is in the AGC loop will control the AGC level, so the important consideration is filtering prior to this power detector. This also applies to narrow band interference---- consider a strong interference that is outside the signal bandwidth but inside the bandwidth that reaches the power detector--this interference would then control the signal level! Often AGC's are implemented in two stages for this reason: there is an analog AGC to ensure the signal (which would be signal plus all noise and interference) presented to the ADC input does not saturate the AGC and optimizes quantization noise considerations. Since there is often considerable additional digital filtering to reduce the spectrum to be just the signal of interest and in-band noise, an additional digital AGC after filtering is also required (especially so for multi-band systems where the ADC is quantizing multiple channels).
For all considerations of setting the AGC level prior to the AGC for optimum performance, please see this post: How to adjust receiver gains to avoid saturation and quantization noise to optimise post digital processing?