iMac suddenly slows down when using Adobe programs

You have sufficient storage on that SSD drive. With just 8 GB of memory though, and the increase in demand for operating system resources from Big Sur, you won't be able to run several large resource-demanding applications concurrently.

For instance, Adobe's minimum memory requirements for each of Lightroom and Photoshop are 8 GB apiece, and the preferred available memory is double that figure. You are attempting to use both in 4GB of available RAM after Big Sur consumes its share.

You are also under-configured for Graphics processor (GPU) memory, as Adobe sets a minimum of 2GB for each of Lightroom and Photoshop and double that for each when using a 4K or greater display.

Your six-year-old SSD may be slowing down from natural causes or may have some need for you to boot into Recovery (⌘+R) and run Disk Utility First Aid on it. If you have never done this, it may be a good idea.

You may, or may not, have malware installed on your Mac. I would recommend downloading the free Malwarebytes, let it determine if malware is detected and removed, and then from the Malwarebytes Help menu, uninstall it too. If you don't, its 14-day full-featured trial will run at elevated system privileges and consume operating system resources that you need for the Adobe products.

And then there is Kurt Lang's recommendation for uninstalling and reinstall the current Adobe Photoshop 2021 product.

Once all of the above has been accomplished, your iMac will have been provided every opportunity to run Adobe products as optimally as it can for its configuration, which may not be enough for your current workflow.

8GB is a bit low for LightRoom and Photoshop and it is not upgradeable on that computer. If you don't have an SSD you might consider getting an external SSD and boot from that to speed things up. Other than that, there is not much you can do on this computer.

As Keith noted, you don't have enough RAM installed for what you're trying to use the Mac for. 8 GB is only sufficient at best to run Big Sur and a few smaller, non-system taxing apps. Like a web browser and email.

When you run large apps like that in cramped RAM space, it's going to end up swapping data to the drive. Swapping will always slow a system down. And as fast as an SSD is compared to a hard drive, it's still much slower than RAM.

As far as the latest Macs being available with 8 GB of RAM? Apple does that for the same reason every single computer maker does, no matter what OS it's running. It's to make a low budget option for people who want to spend as little as possible. And that's really all any low end (least expensive) computer is good for. Basic, simple use.

The new 24-inch M1 iMac can be ordered with 16 GB RAM. The new Apple M1 chip handles RAM differently than does an Intel Mac.

On your 8GB RAM iMac, the operating system will use up half of that RAM leaving you with just 4GB of RAM for your Adobe applications to use. That is I nsufficient and your Mac is swapping to your internal drive to use that secondary storage as substitute for the lack of RAM, and it is much slower. Result: your Adobe applications will crawl. More so, if your internal storage is nearing exhaustion.

I'm not arguing. I'm simply answering your comments with known information.

Since it seems Photoshop is your only problem app, go to the /Applications/Utilities/Adobe Installers folder and run the Uninstall Adobe Photoshop 2021 option. Then reinstall Photoshop via the Creative Cloud app.

I understand that the OS is taking more and more space, but look how much space I still have on the disc for example! Does it not make any difference?

No, not really. Applications reside in RAM when at all possible. A drive is storage, not working space.

I bought this iMac because of the size and not because of the price. There shouldn't be a quality difference between two sizes, not so much at least. I don't know anybody who buys an iMac just to mail and use the net on it.

I wasn't directing that part specifically to you. But yes, lots of people buy a computer for basic, home use. Email, web browsing, home financial apps, etc. Apps that don't take much horsepower or RAM to run.

And there isn't a quality difference. The difference is capability.

Exactly which model and how much memory do you have?

You are welcome.