The version of GoToMeeting that is available in the Microsoft Store is designed for Surface RT tablets, which is why it has limited functionality. Since you are using running a regular full Windows 10 installation you should delete the GoToMeeting software you installed from the Microsoft store and install our regular desktop software.
You can install the regular desktop software from this support article, the process will install GoToMeeting and connect you to a test meeting. Do not worry about the meeting never starting, as long as you see the Waiting for Organizer message the process has been successful. The next time you join a GoToMeeting the desktop software should launch instead of the web based version.
Thanks @GlennD I uninstalled the one from Microsoft Store.
If I click on the link that says download under the Windows icon on that article you sent, it just opens the web based version.
Also, the article, which appears in Spanish since it's my main language, seems only to talk about the web based version explaining things for Chrome, Firefox and Internet Explorer.
It's really being stubborn about this. In the control panel of the web app, there is an option to switch to the desktop software. In the next meeting you join, click on this button to switch and it should become the default for your future meetings:
@GlennD I have never seen those options. I had a meeting today but saw none of that. It speaks about using drawing tools, that seems to be for the host/presenter not for an attendee which is my case.