Why spinning beachball so often? (MBP 9,2 mid-2012 13" i5)

[macstatic]

For some reason I keep seeing the spinning beachball ever so often. And we're not talking high loads either (basically ordinary things like surfing the web, checking email etc.).
I typically have 2-3 apps open (Firefox, Mail, Safari and perhaps TextEdit or iTunes). All relatively light tasks, and the websites aren't heavy video related pages either, but basically a few tabs from forums like here.

The spinning beachball often appears when I quit an app (for instance, when quitting Firefox I might get 10 seconds of the spinning beachball before it's actually fully quit).

I really can't make sense of this because my setup should IMHO handle this just fine. Here's my configuration:

• MacBook Pro 9,2 (mid-2012) 13", 2.5GHz i5 processor
• 16 GB RAM (two 8GB 1600MHz DDR3 memory modules)
• 2TB Samsung 860 EVO SSD (currently around 25% full)
• MacOS 10.13.6 (High Sierra)

Several years back I read about the failing hard drive connection cable, and I had it replaced under warranty. I had completely forgotten about it until I read this thread where people talk about slow drive access. Is the drive cable a weakness on this particular machine meaning it could break again?

 

[MBAir2010]

could be the cable
but
Mine spins when i start the macbook pro non retina 2012 i7 16gb ram after the screen saver approaches,
then Monterey launches safari, mail, music and then weather programs, then things are fine.
on my second drive, Mojave starst great and runs perfect
until i use safari and high ram websites suffer to start video, but then do.

high Sierra was the worst OS X i ever used and needed much RAM for photos and other apps,

i replaced the cable back in October and added a second drive (under $8) in January.
the reason for the cable replacement was the MBPro did not boot and has a text code on the display after booting.

I hoped this help and let us know if you need more assistant
these are great macbook still, even today!

 

[macstatic]

With the cable in mind I ran Blackmagic disk speed test but if I'm not mistaken it all looks fine. I tried it with both a normal login and a safe boot (holding down SHIFT while the computer starts up) but the numbers were about the same:

Interesting to hear about your experiences with High Sierra. So you've experienced that management has been better in other MacOS versions?
I still use some 32 bit apps that can't be upgraded, but am torn between that and the fact that I'm missing out on a lot of other apps that need later OS versions, so I'm currently looking into virtual machine setups for those older apps while upgrading to MacOS 10.14 or 10.15.