Create a new grid layer from a CSV, given the four corner coordinates

A very fast solution using, using the Field Calculator is:

1. Import the CSV file as a point layer using LAT1 and LONG1 as X and Y;

2. Save the shapefile as temporary (to be able to add a new field in the Attribute table) (we call here, for the example, VPOINTS);

3. Open Field Calculator and create a new Field (string, field length 250) called "polygon" using the expression

   concat("Lat1", ' ' ,"Long1", ', ', "Lat2", ' ', "Long2", ',', "Lat3", ' ', "Long3", ',', "Lat4" ,' ', "Long4" )

4. With this new field in VPOINTS, in Processing you can use the algorithm Geometry by expression to create a new vector layer with the expression

geom_from_wkt( 'POLYGON(('|| 
"polygon"||'))')

Use VPOINTS as Input Layer and choose Polygon as Output Geometry Type.

The grid is ready and in his attribute table you have all the original attributes preserved.