It's just familiarity. I use Firefox on macOS and I always think the fonts look fuzzy on Chrome when I'm occasionally forced to use it. I spent a few weeks on Arc (Chrome-based) earlier this year, got used to the fonts, and then they looked a bit weird when I came back to Firefox.
I'm surprised Mac users are noticing a difference though, I find the difference basically vanishes on really high res displays (like my QHD-ish panel on my Framework 13).
Interesting, font rendering is the number one thing that makes me hate Electron apps (I have so much more reasons to hate Chrome).
It’s to the point that I just can’t use, say, VS Code on a monitor that is not Hi-DPI.
Don’t get me wrong, I’m not saying that the font doesn’t look better. Maybe it’s aesthetically more pleasing but to me, it’s just harder to read.
I have multiple eye issues that may not help and which make me more demanding but since I don’t have this issue with OS rendered fonts, I consider this to be an issue.