Documention Meeting Invitation Process (free/busy)
https://help.gnome.org/users/evolution/stable/calendar-meetings-sending-invitation.html.en states:
To schedule a meeting:
12. To query free/busy information for the attendees, click the Free/Busy button on the toolbar, or click Options ▸ Free/Busy.
In my Evolution 3.28.2, in the window where the meeting is created, there is an "Options" menu, but it lacks a "Free/Busy" element. The documentation shall mean "... or click the 'Schedule' tab".