Google Sheets is breaking the mold and has removed the Add-on menu. Now you will see “Extensions” instead. Locate the new menu to the right of the Tools menu and to the left of the Help menu.

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Add-ons
Instead of an Add-ons menu, there is now an Add-ons option under the Extensions. This first option will allow you to add new Add-ons. (I code Add-ons! Check out two that I have created and install them in your Google Sheets.)

TemplateTab: Create a sheet per student on your roster in the same spreadsheet.
toTabs: sort Google Form data into individual tabs.
NONE of my Add-ons collect user data. No PII. You only authorize yourself access to your own files.
Macros Have Moved
Macros used to be under the Tools menu. The Tools menu is still there, but the Macros are now under the Extensions menu. This allows you to automate tasks in Google Sheets.
Apps Script
You no longer have the “Script editor” (something I use multiple times a day). Now Google Sheets is letting you know that you are able to code Google Apps Script for this spreadsheet. Same functionality, new title.
New Menus
The Extensions menu is new, but the old menus are redesigned! This is going to feel like driving a rental car for awhile… how do I turn on the windshield wipers on this car?