Chart: check alt text by hand
Why it matters
Charts need a text summary, and Google does not let add-ons read chart alt text.
How to fix it
Open the chart editor, go to Customise › Chart & axis titles, and add a description. Summarise the main trend nearby too.
Google does not let add-ons read this setting, so Legibright cannot tell whether it is done. Follow the steps above, then mark the item as OK.