Network connections come with priority scores that determine in which order to connect. Sometimes, the default order is not satisfying, e.g. if you want to prioritize your mobile hotspot or home network over some public connection. In Ubuntu (tested on 20.04 with Gnome 3.36), the default settings don’t allow you to change the order. Luckily, there is a GUI accessible without installing anything.
Open a terminal and type:
nm-connection-editor
This launches a window containing the list of your networks. You can edit your preferences by double-clicking on a network name. Then, in the “General” tab, you can change the number associated to “Connect automatically with priority”. Higher number means higher priority.