YouTube has introduced “Consistent volume” on its Android and iOS platforms for YouTube Music. The feature normalizes volume across tracks, reducing jarring differences in volume for videos. This quality-of-life improvement is now available in the Settings > Playback section. However, it’s not yet widely rolled out, with only iPhone users having version 8.15. Users have long requested this feature, which can be toggled on/off via in-player settings or accessed through the settings menu.
Source: https://9to5google.com/2025/04/18/youtube-music-consistent-volume