The info below is from my archives.
You'll note that it dates from 'way back in Mojave -- it may not even be relevant any longer (others please comment if that's the case).
But... it MIGHT help you.
I suggest you try ALL FOUR settings, to see if they make any difference. You MUST log out and then log in after each change to see the results:
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Mojave:
RE-enable subpixel antialiasing for non-retina displays:
defaults write -g CGFontRenderingFontSmoothingDisabled -bool NO
Then log out and log back in.
Enable subpixel antialiasing smoothing:
Light font smoothing:
defaults -currentHost write -globalDomain AppleFontSmoothing -int 1
Medium font smoothing:
defaults -currentHost write -globalDomain AppleFontSmoothing -int 2
Heavy font smoothing:
defaults -currentHost write -globalDomain AppleFontSmoothing -int 3
NO font smoothing:
defaults -currentHost write -globalDomain AppleFontSmoothing -int 0
Source article:
Apple's macOS Mojave disables subpixel antialiasing, also known as font smoothing, by default.
www.howtogeek.com
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If the above doesn't help...
You might try a DIFFERENT display cable, or a different "connection scheme".
By "different connection scheme" I mean use the MacBook Pro's HDMI port instead of USBc.
Does the display offer other inputs than displayport -- such as HDMI?
If so, try them.
If NOTHING you try helps, then my suggestion is to replace the 1440p display with a 27" 4k display. This will show up "in default mode" on the Mac as "looks like 1080p" -- HiDPI mode.