I haven't used Macs much, but I've also had issues with multi-monitor window placement on Windows and Linux too. I use a Windows laptop at work with a single external display. For some reason, if I unplug the display to go to a meeting, when I reconnect it all my windows are still on the laptop screen, and new windows even open on the laptop screen despite the external being primary. I've resorted to just disabling the laptop screen unless I need it to screen share in a meeting.

At home I use Linux Mint and also went back to one monitor. It seems like the entire desktop is just spanned across both displays, so Windows seemed to always open on the left-most monitor. Maybe it's better now, it's been a while since I tried it. But I'm also visually impaired and use the screen magnifier, which is awful on multiple monitors. If you set the mouse to always be in the center, it centers it across all monitors, not your primary monitor so your cursor is between the two monitors. On Windows, the magnifier app centers the cursor on whatever monitor it's currently on, which I think is much more intuitive. I've noticed this same behavior across multiple DEs (Cinnamon/Gnome & KDE) so I suspect it's a deeper issue. I've thought about making some code contributions to improve the usability but I just haven't spent the time to get a dev environment set up.