So, probably not the OS and not the hardware? I'm literally clueless at the moment and desperate for any solution. I run Apple Hardware Test and got the reference code ADP000. In addition, I installed a new pair of RAM. I've opened the machine, and checked for any possible physical damage to the hardware but can't find any.

I decided to reinstall Catalina again, however, It's not getting better. I decided to reinstall the OS that came with the computer (Mountain Lion), and it's still the same. It takes forever to do internet OS recovery* and install a new Catalina and I keep bumping into the same problem. Turn off unneeded Login Items, uninstalled apps, cleaned junk, cleaned malware, and check+ and repaired the storage via Utility Disk until I decided to wipe out my SSD. I tried my best to do some possible actions I can find online to solve this. Even to type something it takes 10-15 seconds until it appears on the screen. However, it needs at least 20-30 seconds to respond to a single click or hover. The cursor is still responsive and has no problem. Last week, I forgot to turn off my Mac while I commute and when I got back home and open the computer, it started to become unresponsive.

In the last 9 years, I almost always turned off my Mac every time I put it in my rucksack (I know it shouldn't be a problem, it is just a habit). I have upgraded my storage to 500Gb SSD and also my RAM to 8GB. I still using MBP Mid-2012, and it works just fine for more than 10 years until a couple of days ago.

2012 macbook pro 13 i7 8gb