Lightroom Classic performance on macbook

Question

Hey everyone, hitting a wall here and hoping someone might have run into this or found a workaround.

I’m on an M4 Pro MacBook Pro (24 GB, macOS Tahoe 26.6.2) running Lightroom Classic v15.5.1 and Premiere Pro. Lately, heavy workflows like AEB HDR merges, timelapse exports, and video renders have ground to an absolute crawl.

The weirdest part? My fans stay completely dead silent. The laptop isn't even breaking a sweat because the hardware isn't actually ramping up.

I ran powermetrics during a timelapse export to see what was going on under the hood:

CPU: 100% maxed out across all 14 cores pulling around 29–35W.
GPU: Pulling a measly ~50 mW (basically idling at 0.05W).
Fans: 0 RPM.

Lightroom is leaving the graphics processor completely untouched and forcing the CPU to shoulder the entire export under a low total power budget.

What I’ve already tried:

Toggled GPU acceleration (Auto, Custom, Off) inside LrC preferences.
Cleared out all preview, scratch, and media caches.
Did a full, clean wipe/reinstall of Adobe Creative Cloud, followed by a clean macOS reinstall.
Verified everything is running off the fast internal SSD (Disk Utility and Apple Diagnostics both pass 100% clean).
Tested in Safe Mode and tried different high-wattage chargers/OEM MagSafe.

Has anyone on Tahoe / LrC 15.5.1 seen this happen where Metal just fails to engage on export? Is there a config flag, terminal tweak, or setting I’m missing to force Adobe to actually use the GPU?

Appreciate any ideas!

Conrad_C · Answer

This might not be the solution, but it’s something to check: I didn’t see any mention of the macOS Energy Mode. I was building 1:1 previews last night for a few folders and decided to do a test.

My MacBook Pro is running the same versions of macOS and Lightroom Classic as yours.

I have the Energy Mode set this way:

On Battery is set to Low Power.
On Power Adapter is set to High Power.

(A fresh install will default to Automatic for at least one of those, maybe both.)

I was curious so I decided to try the previews both ways.

On the power adapter (which I set to High Power), the previews generated extremely quickly, CPU/GPU usage was very high, and the fans got loud (max RPM) although that kept the SoC temperature well below maximum, apparently avoiding any thermal throttling. This is all expected. (It is also why Apple defaults to Automatic because that’s almost as fast but not as loud.)

On the battery (which I set to Low Power), the previews definitely took longer although I didn’t time it exactly. But here were the other effects, that sound a lot like what you said:

CPU/GPU usage was held down, it didn’t look like there was any Super Core activity. (Super Cores are an M5 thing).
Temperatures were another 10 degrees C lower.
One fan was at 0 RPM, the other very low, so of course it was silent.

I have seen a similar difference when rendering video in Premiere Pro/Media Encoder. High Power is fast, hot, and loud, Low Power is slow, cool, and quiet.

If you haven’t checked Energy Mode, either click the battery icon in the menu bar, or open System Settings and click Battery.

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