With a desktop manager like windows and macOS, you can choose specific windows to share. But that is not an option in windows manager like i3. There is an advanced sharing option on zoom to only share part of the screen. Currently it is not working in my linux distro. So is there a way to work around this without second screen or complicated config?
Window managers usually have a notion of workspace that refers to windows groupings. You can only show the programs you need in a standalone workspace if you don't want to show your entire desktop. This is essentially equivalent to showing only one windows. In i3wm, all you need is to send the the current window to a certain workspace you are prepared to share. In i3, you can add the following command to you
bindsym $mod+Shift+1 move container to workspace 1 bindsym $mod+Shift+2 move container to workspace 2
This will allow you to send the current window to a designated workspace.
However, if you have a larger monitor, font size could be a problem. If you want to share cli program, changing the terminal font is the most convenient option. Most terminal have commands for this functionality. In gui program, this should be more straight forward.
So when you need to share screen, first create an empty workspace, then send the windows to the new workspace, finally adjust the font size for the audience to see more clearly.