Check as following:
1.Create a new Canvas app from blank in Power Apps, fill in the app name and select Tablet format:

2.Change the screen Fill and size you want:
3.Then insert Label and Button elements to your screen and fill them with text:
4.Change the RadiusBottomLeft/RadiusBottomRight/RadiusTopLeft/RadiusTopRight properties of Button to make it as rounded corners:
5.Specify the OnSelect property of Button to perform when the user taps or clicks a control.
6.Save it in Power Apps, in SharePoint, edit modern page and add a new section as three columns:
7.Add a Power Apps web part with App web link or ID, find it in Details panel of the specific power apps:
8.Duplicate the web part to other two sections, sample results are for your reference:

Note, this is just a sample without any data connection, If you need to put it into use, it is necessary to add data connections and button events.
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