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