Most Video streming is still done with h264, since this is integrated in hardware chips as encoder and decoder for many years.
HEVC or h.265 is available as hardware decoder for a few years, but encoders are always in software and therefore need a lot of power.
YouTube uses VP9 because Google bought that company and released it as opensource, but it still is extremely compute-intensive for encoding.
The NextBigThing is VVC or h.266, started in 2017 and open source released now: https://vcgit.hhi.fraunhofer.de/jvet/VVCSoftware_VTM
The efficiency is always 50% better per generation, meaning the same looking quality costs 40mbit/s in h264, 20mbits in h265 and 10mbits in h266.
During the bleak state of MPEG licensing, free codecs are on the rise.
AV1 from AOM is 30% more efficient as h.264 and royalty and patent free.