So I thought the issue is the resolution and/or font issues but even after I reduced from 4k to 1920-1080px and/or changing to all font size, the issue is persistent. (Well I tried to troubleshoot for a week now.) I tried with safe mode and photoshop worked fine with any lagging. Well, it is tolerable lagging in the safe mode.
My guess the issue is GPU-related. Like here in thelink, turning off the G-Sync in NVIDIA helped. Since I have GigaByte Radeon Rx 580 8GB, is there any similar thing in the Radeon drive that I can turn off?