Thavius Beck demonstrates how to set a global project key and scale in Bitwig, then use that setting to constrain note editing to only the valid scale degrees. The example uses C minor pentatonic, but the approach applies to any key and scale combination.
Once a scale is active, the note editor highlights the in-scale lanes in blue. From there, you can switch the background display to "adapt to key" so the visual layout reflects the scale, and toggle snap-to-scale on and off with the K shortcut.
With snap enabled, any note you draw automatically lands on a scale degree, skipping the out-of-key lanes entirely. The same toggle is accessible wherever you see the flat/sharp icon in the interface. Pressing K again disables it when you want to place notes freely.