These terminal commands became available back around "Mojave", but as far as I know, they're still relevant:
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
You want to try ALL FOUR settings, to ascertain which works best for you:
1, 2, 3, and 0.
Also remember that you MUST log out and log back in to see each change after you make it.
Hmmmm....
There's also a tool called "Font Smoothing Adjuster", that works without terminal.
See here:
Download the free and open source Font Smoothing Adjuster app to disable or customise font smoothing on macOS Big Sur.
www.fontsmoothingadjuster.com