Need help dissecting EtreCheck results

your Mac is based on a VERY SLOW (5400 RPM) mechanical HDD. I'm not seeing the 28GB flash storage portion of a Fusion Drive. and the HDD appears to be failing. those drives were slow when new, so it failing just compounds the slowness.

the easiest way to speed things up would be to use an external SSD as your boot drive. to implement that, please see Use an external SSD as your startup disk with your iMac or Mac mini - User Tip.

It is definitely your Hard Drive. You have what was called a Fusion Drive that was a great idea at the time, but has a poor longevity, similar to other mechanical hard drives. Make sure to have a solid backup. The solution will likely require getting an external drive and boot from that one. Others here may be able to provide a recommendation or provide further assistance with that setup.

you're welcome. :)