Add Alternative Text (Alt. Text) to Images, Shapes, and Graphs in Excel
Right Select the Image, Shape, or Graph
All of the options are the no matter which you are adding alt. text too. For this article I will be showing how to do this by using an image.

Select Edit “Alt. Text ….”

Describe the Image, Shape, or Graph

In this example you could say “The SNHU logo.” If the image shape, or icon is only decorative select the box to let the screen reader and user know that it is not important to understand the content.
A more in-depth article about adding alt. text can be found here How to Add Alt. Text to Excel (Desktop Mac).
An article how to create useful alt. text can be found How to create Alternative Text.
Use the Accessibility Checker in Excel
Select "Review"

Select "Checker Accessibility"

The most common issue will be missing alt. text from images, shapes, or graphs. This was reviewed previously with a link to add the alt. text. A more in-depth article about using the accessibility checker can be found here How to Use Accessibility Checker in Excel (Desktop Mac).
Create Meaningful Links Within Excel
With the in-depth this goes it would be best if you follow the link to the in-depth article. A more in-depth article about creating meaningful links can be found here How to Create Meaningful Links in Excel (Desktop Mac).
Adding Accessible Properties to Excel Sheets
It would be best to check out the article on this which explains why it is important and how to complete this How to Add Accessibility Properties to Excel (Desktop Mac).
Best Practices for Excel Sheets to Be Accessible
With the in-depth this goes it would be best if you follow the link to the in-depth article. A more in-depth article about best practices for making excel sheets accessible can be found here Best Practices to Allow Excel Sheets to Be Most Accessible.