In Object Mode add a plane with menu Add or Shift+A > Mesh > Plane
Then go to Modifier Properties and add a Subdivision Surface modifier or do the shortcut by pressing Ctrl+3 to add a Subdivision Surface modifier with three (3) levels. Then click the small down arrow > Apply.
Then press tab to go into Edit Mode and press 3 to switch to Face Select mode. Then select the faces as shown below and press X > Faces to delete the selected faces.
Press 1 to switch to Vertex Select mode and select the vertices encircled in red as shown below then press X > Vertices to delete those vertices. Then press tab again to go back into Object Mode to inspect the shape.
Press tab to go into Edit Mode again and select two (2) vertices encircled in red as shown below then press Shift+S > Cursor to Selected. This will put the 3D Cursor right between those vertices. Then add a circle with menu Add or Shift+A > Mesh > Circle. Set the circle's radius to 0.25m
Then select the vertices EXACTLY as shown below and press X > Vertices to delete these vertices. Press A to select ALL vertices and press M > Merge By Distance. Notice that 2 vertices have been merged. Those are the 2 vertices from the circle and 2 vertices from the other shape. Now they are fused together. Press F to fill in a face if you want. Then press tab to go back into Object Mode.