Just upgraded to mpv 0.25. Immediately noticed a bunch of feature deprecations. The 'volume' audio filter and most of the mpv native video filters have been removed (including 'yadif'). The --dvd-* options have also been removed. Major bummer.
The 'volume' audio filter was how you enabled replaygain; now there's no way to access that functionality. It looks like there will be a new option in 0.26 specifically for that.
Checking now I see 0.25 was released 7 days ago, so this is old news.