Freezing of OS, Finder, Slowness

I've previously asked all over the Internet about Finder freezing. The symptoms of this are, well .. as you can guess, Finder no longer responding. Spinning beach ball. I can't open . from the Terminal, and restarting Finder (either by long-press and 'force quit', or by killall Finder from within Terminal) has no effect. Even rebooting the machine via the 'usual' means doesn't work, and it will hang for days. The only solution is to cycle the power, and start again.

So, over the course of the weeks and the months where this was happening, I have noticed that it seems to be linked in some way to my external drives. I have a powered hub in the back of the Mac, and that has four external USB drives. There are also cables for a Garmin GPS, an iPhone, and an SD reader. None of these is automatically mounted, and if I leave them without mounting them, the Mac will happily stay up for weeks.

However, as soon as I start to use them, attaching them, using them and detaching them, then the problems will start.

So .... can anyone shed light as to why this problem happens when I use external drives?

Thanks.

For information: Mac Mini running 10.15.7 (19H1419).

In a previous life I worked for MacWarehouse. They got a contract to answer pre-purchase tech support calls (AS Apple) for a few Apple programs. Part of that was two weeks training as a support tech for the Apple Assistance Center (Apple support before there was "AppleCare"). One of the things I remember (other than "Chooser wars"...) is what they called the first principle of troubleshooting:

"Isolate and Identify."

Which basically means that if you are troubleshooting a hardware problem, unplug everything. And put back any removed/replaced internal hardware if at all possible.

For software issues, disable or uninstall the software.

This leaves you with a stock Mac, as it came from the factory. So no if the problem is still happening then you can blame the OS and/or the Mac itself.

In your case, where you are dealing with external devices, unplug Every. Single. One. of the devices and verify the Mac works fine without them.

If it doesn't then you have an OS/software problem or a hardware problem. So I would back up the system. Wipe the drive and install the OS fresh. Then you verify it works with just the OS and start installing software. After each install verify that the system is working properly.

Once that is done you can restore your documents, settings, etc. and verify it is still working. If so, great, if not, it is likely a settings file that was just restored.

Once you have a working system start plugging hardware into it. One at a time and verify everything works before you unlplug that device and plug in another device.

It is slow, annoying and simple a process of elimination.

As you add back software and hardware you are looking for changes in behavior that you can then easily undo (as you are making ONE change at a time) and verify that change was the problem, whether it was a hub, drive, monitor, application, or whatever.

Your particular issue should yield to this method and if you un-plug everything and the problem persists it is possibly OS-related, or maybe related to a problem with the internal drive.

Which brings up the second most important troubleshooting principle:

Back up your data before you do anything.