I am looking for a simple calculator my Macbook air Monterey that will stay on the screen while doing work.

Launch the Mac's Calculator app. It's a simple calculator that you'll find in the Applications folder.

Then control-click the Calculator icon in the Dock, and select Options > Assign to All Desktops.

If need be, in Calculator you can also click Window > Always on Top.

This will give you more insight into using Apple's standalone Calculator app.

Calculator User Guide for Mac - Apple Support