Chord diagrams are pictures, and a screen reader cannot read a picture. Chord names in square brackets do not fare much better — read aloud, [A7] becomes something like “bracket A seven bracket”, or is skipped over entirely.
Screen reader mode solves that. It shows the same song, with the same chords in the same places, written so that it can be spoken.
Chord names are written out in words. Instead of [A7] you get / A seventh chord -. The slash and dash mark where the chord begins and ends, so it is clear where the chord name stops and the words start again.
The chord shapes become text. Along the top of the song is a line giving the fingering for every chord used, like A chord 2/1/0/0/. That is the same information the diagrams hold, in a form that can be read out.
The diagrams themselves are not shown, since their content is now in that line instead.
💡 Handy hint: This is about being readable aloud, not about being larger. The text is the same size as usual. If bigger text is what you are after, see below.
On a computer, the button is at the top right of the page. It says 👁 VI Song when you are looking at an ordinary song page. Click it and you get the screen reader version, and the button changes to Base Song so you can go back the same way.
On a phone or tablet, tap ☰ {Hamburger menu) and look for 👁 VI Song in the menu.
Screen reader mode is not the place to look. To make a song larger and easier to see, use Text Font Size in Settings, which will make it as large as you like, and set it once for every song through Default Settings.
Other things worth trying on that page: the Low Vision and Dyslexia fonts, Show Songs in Monochrome for stronger contrast, and the various bold options.