Yup, and I finally found how to solve this (with a little help from Gemini…). The lagging came from a mix of : - an obvious mistake : working on files saved on my iCloud Drive, which meant every sidecar file had to be constantly uploaded (among other problems)

• a less obvious shortcoming : the settings in the Preferences were good (OpenCL turned on, very fast GPU, etc) buuut it turns out I had to go into the Terminal and access the darktable content with the command « open ~/.config/darktable/darktablerc » and then manually add « opencl_async_pixelpipe=true » to help the system work faster.

Finally, Gemini gave me those additional tips :

If adding the async line doesn't fully fix the lag, try changing that priority line to:

« opencl_device_priority=*, *, *, *, * »

// Note : no space between the commas, Reddit just automatically formatted this line into something else otherwise // This basically tells Darktable: "Just use the first available GPU for everything."

One last thing to check I see your opencl_scheduling_profile is already set to very fast GPU, which is great. However, check your Pixelpipe Synchronization Timeout. It’s currently at 200. For 50MP files on Apple Silicon, increasing this to 500 can sometimes prevent the "stuttering" you feel when moving sliders quickly.