System Absolutely Crawls

First of all - 2012 Mac Mini is 11 years old.. Please take that into consideration.

Now back to your issues -- since many apps these days do take up larger RAM than year of 2012's apps.

And if you want to keep this machine (I still have mine) - 2012 Mac Mini can take 16Gb memory (and it is user up-gradable). Just make sure you get it from reputable vendors (such as OWC or Crucial) because Macs are very picky with RAM. (just checked OWC, 16GB memory costs about 36.99 USD).

Second, your Mac Mini probably equipped with 5400 rpm HDD - this would also create a bottleneck.

If you are handy enough, you can follow some on-line DIY and change into SSD (again, OWC carries reputable SSD).

However, I would not spend lots of money on this machine..

Best of luck

No, it's not normal. Please determine if the same problems occur in "Safe Mode": Use safe mode on your Mac - Apple Support.

Steve314 Said:

"System Absolutely Crawls"

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I see you have 4GB of RAM --that is not intended for multitasking. So, that may be making this occur.

On top of the small amount of RAM, if you just upgraded macOS, there is a chance that Spotlight is doing a complete re-indexing of your disk.

I came across that somewhere in the Snow Leopard > El Capitan > Sierra > High Sierra path, and the computer absolutely crawled for a day or two until Spotlight was done with going through the entire disk. (At least, it appeared to be Spotlight.)

> HDD: 500 GB (Rotational)

As already said, this is the main reason. APFS is VERY slow on HDDs.

Your options are to use SSD as a boot drive (internal or external) or downgrade to High Sierra which supports Mac OS Extended. And optionally also upgrade RAM to 8-16 GB.