Fonts blurry on external monitor

MacBook Pro (15-inch, 2018), it has good Graphics Radeon Pro 560X 4 GB

Connection cable: a good MOSHI USB-C to DisplayPort Cable, Supports up to 5K/60Hz resolution

External monitor: tested several non retina external monitors, all set to DisplayPort 1.4, tested 4k monitors and QHD (2560x1440x60Hz), results are same to all external monitors: blurry fonts, crap text displayed on external monitor

macOS Big Sur version 11.6 (20G165)

Issue: macOS Big Sur displays blurry fonts on external monitor

Tried on terminal:

• defaults -currentHost write -g AppleFontSmoothing -int 0
• sudo defaults -currentHost write -g AppleFontSmoothing -int 0
• reboot

After reboot the MacBookPro it is the same blurry fonts. It seems the change on the variable (AppleFontSmoothing ) is not persistent, which is confirmed by typing on terminal: echo $AppleFontSmoothing (it should return the stored value zero but returns null, meaning no permanent change was stored on the variable).

Tried also:

• defaults -currentHost write -globalDomain AppleFontSmoothing -int 3
• reboot

Googled "big sur blurry font external monitor" and it seems everyone having same issue

Any solution?