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Depending on how large your display is, it may either not be HiDPI at all or it may require fractional scaling which is currently unsupported. You might find this article interesting: https://medium.com/elementaryos/hidpi-is-more-important-than-4k-b1b9bb110b43

Unfortunately we have no control over 3rd party apps that are inherited from the Ubuntu repos or sideloaded from the Internet. All of the apps in the “Curated” section of AppCenter should automatically adjust to the system scaling factor.

We don’t support or provide a tweak tool and we don’t intend to add a setting to move or change window controls.

If you’re having issues with Epiphany or would like to file a feature request, they track issues on GitLab here: https://gitlab.gnome.org/GNOME/epiphany/issues

Can you be more specific about which applications you’re having this problem with? There should be a fairly wide 12px area around window borders where you can drag to resize

The lack of a settings dialog is intentional. All of Files’ settings are contextual. You can see free disk space by hovering over a disk in the sidebar or by right clicking any view and selecting “Properties”. You can see information about a selection by hovering over any file in that selection. There is an overlaid statusbar in the bottom corner of the window. Files uses a single click model instead of double click. You can right click any file or folder and select “Rename” to begin editing.

This issue with system settings is likely a result of changing font sizing to work around your fractionally scaled display.

There is absolutely no intention to look like macOS. If you feel like elementary OS is different from macOS that is good and intentional.