Based on CRF Guide (Constant Rate Factor in x264, x265 and libvpx), quoting:
Streaming nowadays is done a little more cleverly. YouTube or Netflix are using 2-pass or even 3-pass algorithms, where in the latter, a CRF encode for a given source determines the best bitrate at which to 2-pass encode your stream. They can make sure that enough bitrate is reserved for complex scenes while not exceeding your bandwidth.
also the article Saving on Encoding and Streaming: Deploy Capped CRF also claims that "Capped CRF" is the highest quality while also making sure bitrate does not go above X but they propose a single pass with:
ffmpeg -i input_file -crf 23 -maxrate 6750k -bufsize 6750k output_file
What's the correct way to generate the highest quality possible file inside a bitrate constraint using ffmpeg with x264?