AME h264 wrong bitrate video (music + still image,no transition) for youtube

Hey!

I have music video(music + still image, no transition) for youtube.I made it in after effect. Send it to AME and render it with settings in image below.

I set bitrate to 50 mbps in CBR or VBR(2-pass)  but exported video has only 10-15 mbps. I try different background images but i can't get over 10-15 mbps bitrate. Also i upload it to youtube(with 10-15 mbps bitrate) but it has poor quality even if it has still image with no transition.

In video, any quality is poor/blocky except 1080p on youtube.

My exported video is here : https://www.youtube.com/watch?v=9giojaeFJoc

example videos from another channel : https://www.youtube.com/watch?v=rSooWgytpA0

https://www.youtube.com/watch?v=DMIggl34m78

You see no blocky pixels in any quality (720p or 1080p)

how do I solve this issue?pls help me 😕😕