If Artie's suggestion doesn't work (and I should have thought of that myself), go to System Preferences>Appearance and play with the font settings at the bottom. My system looks fine and my settings are:

(Box checked) Use LCD font smoothing when available.
Turn off text smoothing for font sizes 8 and smaller.

Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365