Hey NongThan!
Thanks for the info, although I think the moderator needs you to remove the serial number (as any other personal info).
Anyhow, can you say if this “lag” starts while using any specific apps, or doing any activity in particular?
Do you get the spinning wheel a lot when this happens? And do you have to force quit the app(s) when this happens, or even restart the Mac?
I think the best two tests for this problem is:
A):
Testing in another user account:
Set up users, guests, and groups on Mac - Apple Support
And:
B): Testing in Safe Mode:
Start up your Mac in safe mode - Apple Support
This may help to narrow down the cause from either a system wide issue (The OS or file system), or a user profile issue, (A setting, preference, permission or login item issue).
Likewise, I do find Activity Monitor useful at times to find a rogue app or process that maybe causing the problem:
Activity Monitor User Guide for Mac - Apple Support
Another good test would be disconnecting any or all externally connected devices, and restarting, this is a good way to rule out if one of those devices is causing an issue.
Hope something here helps! It may not solve the problem, but may point you and/or us in the right direction!