Disable auto resizing of windows when dragged to the top and/or screen edges

Open Terminal and run

gsettings set org.gnome.mutter edge-tiling false

You may also have to run

gsettings set org.gnome.shell.overrides edge-tiling false

Alternatively, if GNOME Tweaks is installed, going to Windows there is an option named Edge Tiling...just disable it ― the result is the same.