Slow iMac crashing for most intensive apps, specifically Adobe Lightroom (wont open)

Notes:

• Delete Webroot and all other anti-virus and web-protection apps.
• No Time Machine backup. Backing up is important!

Here's your main problem:

Performance:

System Load: 1.63 (1 min ago) 1.73 (5 min ago) 1.70 (15 min ago)

Nominal I/O speed: 0.84 MB/s

File system: 45.67 seconds

Write speed: 55 MB/s

Read speed: 60 MB/s

I don't know how you didn't notice performance issues earlier. The reason your iMac is very slow is due to the 5400 rpm hard drive. Very slow. If you use an external SSD and run macOS from that, it will make your Mac 10 to 30 times faster for storage. For more info, instructions, and what external SSD to buy, please read: How to Setup and Use an External SSD as y… - Apple Community.

-Jack

Hello, wallphotog.

Sorry to know you're having this trouble.

I looked at your EtreCheck report. You did well to get it posted. Thanks.

Potential Problem - Webroot SecureAnywhere - Suspect. Active anti-virus app potentially troublesome. If this was installed after the fact of the slowdown, then obv not causal.

BIG Problem - Mechanical HDD @ 5400rpm

Read/Write drive speeds are very low @ 60/55 MB/s for the tasks you want to accomplish, though about normal for this type of drive.

This needs to be upgraded to an SSD if you want the performance you need to do the job you're trying to do.

Adobe Creative Cloud apps will likely tax the machine, and the slow drive is definitely a bottleneck. At minimum you want a 7200rpm mechanical HDD to avoid this.

You were running Catalina at the time you experienced the slowdown? Your upgrade to Big Sur will likely exacerbate the issue. I strongly suspect the HDD. Have you run Disk First Aid?

Also make sure your backups are up to date.

Otherwise, I see nothing else that jumps out as a potential bad actor. Maybe others will.

First, there is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac.  This user tip describes what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community.  

There are no known viruses, i.e. self propagating, for Macs.  There are, however, adware and malware which require the user to install although unwittingly most of the time thru sneaky links, etc.   

Anti Virus developers try to group all types as viruses into their ad campaigns of fear.  They do a poor job of the detecting and isolating the adware and malware.  Since there are no viruses these apps use up a lot of system resources searching for what is non-existent and adversely affect system and app performance.

There is one app, Malwarebytes, which was developed by a long time contributor to these forums and a highly respected member of the computer security community, that is desshoigned solely to seek out adware and known malware and remove it.  The free version is more than adequate for most users.  

Also, unless you're using a true VPN tunnel, such as between you and your employer's or bank's servers, they are useless from a privacy standpoint: Public VPN's are anything but private.  

I would recommend you uninstalling webroot and any other cleaning or optimizing apps that yo may have according to the developer's instructions.

If you're worried about malware then MalwareBytes is the only app I'd use.

Ok, but still delete Webroot. It is junk on Macs and only damages your system. The only anti-malware that is recommended is Malwarebytes for Mac (free).

What SSD are you planning on purchasing? Some don’t play well at all with Macs.

-Jack

As to why Adobe Lightroom won't open at all; I would try to delete the App (not your work/library), and try to reinstall Adobe Lightroom.

-Jack