Other than the new sheet button which method can be used to add an additional worksheet to the workbook

backstage view
format tab
insert tab
worksheet context menu

worksheet context menu

Explanation:

You are just required to right-click on the sheet name mentioned below in the worksheet. By plus button, you can add a new sheet. However, if you right-click over the sheet name then as well you will get a worksheet context menu, and there you will find the insert option at the top. If you will click over on it, you will get an option to add a new sheet, macros and a few others. And from here as well you can add a new sheet. Hence, the worksheet context menu is the correct option.

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