When to use gain versus equal power crossfades

Equal gain is linear. Equal power is more sloped.

Use equal gain (linear) when the audio on both sides is coherent (that is, the audio within the crossfade region is the same in both tracks).

Use equal power (curved) when the audio on both sides is not coherent (maybe similar, but quite different upon close inspection, e.g. non-continuous background noise).

Each of these best practices ensures a consistent level across the fade.¹

This article may have more to offer too: https://www.soundonsound.com/techniques/using-fades-crossfades?utm_source=pocket_mylist