Can I link an external GPU to iMac to handle raw files?

Apple Silicon Macs don't support the use of eGPUs.

That was an option with some of the later Intel-based Macs that had Thunderbolt 3 ports, but the architecture of Apple Silicon Macs is based on all types of computing units having access to all of system memory. If you want a better GPU, instead of adding an eGPU or PCIe card, you start out with a higher-end processor chip which comes with more GPU cores.

I suspect that this assumption is pretty deeply ingrained in the current Apple Silicon versions of macOS, because even the current desktop Mac Pro – with its M2 Ultra processor and PCIe slots – does not support PCIe graphics cards!!! That's a very radical evolution from the previous Intel-based desktop Mac Pro (2019), a minitower which was explicitly designed to support high-end PCIe graphics cards and MPX graphics modules.

beagle41 wrote:

My IMac has worked well for my purposes up to now: using photoshop, lightroom, and premiere to work with smaller files.

But my new Sony A7r4 shoots 60 mb raw files...if I use the Pixel Shift feature they expand to over 100 mb.

Then when I stack 4 or more images in Photoshop to further process, the computer slows down, then freezes.

I wonder if the problem is that you do not have sufficient RAM for your new, heavier workload.

Could you start Activity Monitor (Applications > Utilities > Activity Monitor), click on the Memory Tab … and then watch the Memory Pressure graph as you do the things with Photoshop and Sony A7r4 Raw files that cause your iMac to slow down and freeze?

That graph is color-coded:

• Green means that the amount of RAM is likely sufficient for what you are doing
• Yellow means that the amount of RAM is marginal for what you are doing
• Red means that the amount of RAM is insufficient for what you are doing

If you see a lot of Yellow or Red appear on that graph, that could be an indicator that you're now asking the Mac to do too much (relative to the amount of RAM it has). A high "Swap Used:" figure could also be cause for concern.

Please read the following user tip and restate your question/problem in detail: 

     Writing an Effective Apple Support Communities Question - Apple Community

How much free space do you have on your boot drive?

What app are you using to mange the large RAW files?

What happens when you try to use a RAW file?

How big are the RAW files? (As a point of reference I have a 2017 i7 iMac with 16 GB of RAM and are able to open and edit a 500MB image file with Photoshop Elements. There is a slight delay when using its blur tool but other edits have no problem.)

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

You may to review this article on the Adobe site, to see if there are any tips there which help with your situation.

Adobe – Optimize Photoshop performance

Old Toad wrote:

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

beagle41 wrote:

Your suggestion of using optimizing/cleaning programs seems the next step. Do you recommend a brand ?

Thank you again.

I could be mistaken, but I do NOT believe that Old Toad was recommending that you use such programs! Unless I miss my guess, he's one of the posters here who believes that such programs often CAUSE performance issues or other problems for Mac users. Thus, if you answered his question with a "Yes", I believe that his suspicions would immediately fall upon the application(s) in question.

No, I was asking because those types of apps are totally not needed by Macs and can and have done harm to the system and other apps. I should have made that clear with my first reply.

I tried a demo of the App Cleaner & Uninstaller and feel it is safe to use. However, if you use App Cleaner & Uninstaller on an app that you have other apps from the same developer, like Adobe, you must be extremely careful deleting.  Some for those files may support other apps from the same developer and deleting them can mess them up.  Adobe apps is a primary example. I know from experience.  For singular apps from a developer it's safe.

However, Mac Cleaner Pro is another matter. I would not use it under any circumstances. Apps like that can damage other apps and the system by deleting what it thinks is a nonessential file or duplicate file which is needed. I recommend you uninstall it according to the developer's instructions.

How much Free space do you have?

App Cleaner & Uninstaller, which is my goto cleanup app…

https://nektony.com/mac-app-cleaner

Mac Cleaner Pro...

https://nektony.com/mac-cleaner-pro

App Cleaner & Uninstaller always seems to cross check if any other Apps, same developer or not uses the files to be deleted & has warned/asked me.:)

That's good to know. Thanks.