Rounded Rectangle Tool missing

The accepted answer is misleading. The rounded rectangle tool is still an option in Illustrator as of today. It's just no longer a default tool in the toolbar. If you click on the three dots at the bottom of the toolbar (...) to open the toolbar options, you will find the rounded rectangle tool right there to use and add to your tools whereever you would like. "No longer needed" is also incorrect, because while you can drag the handles on a single object to round the corners of a rectangle, making multiple rounded rectangles with the same radius would be a tedious chore without the rounded rectangle tool.

In version 22.3 the rounded rectangle tool has been removed. It is no longer needed as the standard rectangle tool can now do rounded corners. Just drag the handles

Dave

That's a well thought out screen shot I must say.  It answers an obvious question you were likely to have been asked.

OK, any reason you are still using version 21. ?  Is it an operating system issue like you have an earlier version of OSX that won't run v22?  If not, then updating it always going to be your first best bet.

I am usually loath to suggest resetting Preferences until all else has been tried, but in this case, I think that's what I would do.

If resetting Preferences does not fix it, then we will need to know what operating system you are using.