How to add a Notes to Matrix visual values if you hover over it

Hi  pbidaxlearner
Unfortunately, we don't have a notes object that is possible to use on every cell like in Excel in power bi.
But we can use tooltips. The option to muse it from columns heather is to add some button to every header and modify your notes on it :
For example, you can use a kind of "help" button.
Format it in the way you want.

Turn on the action and choose bookmark with none, just to modify your text note:

Hi pbidaxlearner 
Inforiver (the table from the attached tutorial) and Zebra are 2 applications with much more possibilities than the generic tables and matrixes that we have.
But they are for pay.
For more information, you can visit their sites:
https://inforiver.com/matrix/

https://zebrabi.com/power-bi-custom-visuals/tables/

Back to the case of your multiple columns consider using bookmarks to show and hide some glossary about your table.
You can go to my published link and play with the buttons.
https://app.powerbi.com/view?r=eyJrIjoiMDdkYzRmZjYtMjU1MS00MTExLThhNTQtYzQ2Y2Q0NTIwYTE5IiwidCI6IjA3YTk2YWU0LWJkYTgtNGM5Yy1hMGYxLTY1ODVjY2ZmMmRlNyIsImMiOjl9
The tutorial for modifying is here:https://www.youtube.com/watch?v=7DuNAgiyIQU
Also updated a sample file from the previous answer.

Link to a sample file:link to pbix 

If this post helps, then please consider Accepting it as the solution to help the other members find it more quickly

Hi pbidaxlearner 

As i mentioned in previous responds.

This option doesnt exist in power bi unfortunately .

All others are alternatives:

1 Addins like zebra / inforiver

2. Buttons from my first answer

3. Bookmarks from last one.

You can vote it as idea here:https://community.fabric.microsoft.com/t5/Ideas/ct-p/PBI_Comm_Ideas