The built-in Gnome screen recorder does have limitations:
A better full-fledged screen recorder is Kazam.
CTRL + ALT + SHIFT + R
This will immediately start recording the desktop.
A red dot will be displayed in the system tray area of the top panel.
The recordings are saved in webm format in the Videos folder.
CTRL + ALT + SHIFT + R
The maximum recording time, by default, is just 30 seconds.
Increase it:
gsettings set org.gnome.settings-daemon.plugins.media-keys max-screencast-length 300
This increases the maximum length of the recording to 5 minutes.
Change it to 0 to not have a limit.