Quick take: Levels isn’t broken—you’re not on editable pixels or you’re in the wrong mode. Start with Layer 0.

First, the ActionSeps™ baseline (must match this):

  • Single layer, named “Layer 0.” Unlock/flatten so you’re editing one raster layer.

  • Rasterized. No Smart Objects or live effects (Right-click → Rasterize Layer).

  • RGB / 8-bit. Image ▸ Mode ▸ RGB Color + 8 Bits/Channel.

If Levels is still greyed out or does nothing:

  • Not pixels? Text/shape/mask selected → switch to the layer thumbnail (pixels) or use a Levels Adjustment Layer.

  • Smart Object? Layer ▸ Rasterize ▸ Smart Object, then apply Levels.

  • Stack is messy? Stamp a fresh working layer (Shift+Cmd/Ctrl+Alt+E) and adjust that.

  • Running via Actions? In Actions panel, toggle Dialog On for the Levels step to set values manually.

See also: /fix-command-select-not-available-photoshop, /need-help-separating-actionseps