As of release v0.29.0 the usage of opengl-cb API is deprecated:
https://github.com/mpv-player/mpv/releases/tag/v0.29.0
https://github.com/mpv-player/mpv/blob/5feee11e43a0907306db1df993cf1cd11c8596d9/libmpv/opengl_cb.h#L22

The replacement for opengl-cb should be the "render" API.

https://github.com/mpv-player/mpv/blob/master/libmpv/render.h