I have been convincing myself I'm going nuts, but finally worked it out.
I have three screens:
- One WXGA+ old one, that I run my email and Microsoft Teams on.
- My laptop Screen (2015 MBP 13" Retina) that I use for what I'm referring to.
- One big 1080p screen that I do my main work on.
When I write a new email, the Mail app is on my 1440x800 screen, but it pops up the "Compose email" window on my Retina laptop screen. In doing so, it appears to use non-retina graphics for the compose email window, so the text is blurry and ill-defined. If I move that window off the laptop screen to one of the others and back again, it's nice and crisp again. It's pretty subtle, so for several weeks I've been chalking it up to me just getting old.
Anyone else noticed this?