Whenever making any setting change, especially ones that we can look at what the change does, for example font-family, it becomes difficult to check on smaller screen sizes since the settings modal hides most of the note behind.
Now that Obsidian can open new windows, it only makes sense that the setting is a window by itself so it can be dragged and resized separately while looking at the changes in the notes/interface behind clearly.
There’s no workaround for this presently, except to keep opening/closing the settings modal after checking if the changes were satisfactory. Some plugins like Style Settings, which have config for many themes, can open in a new pane which is slightly useful since that pane can be dragged to one side. I guess settings could open in a new pane as well which is set to be in a new window by default.