Tube is broken out of the trunk sheet metal. Looks pretty minor, you might be able to just run a bead around the end of the tube to weld it to the trunk floor to get rid of the crack.
But you’ll need to clean it up better, and if you try to do that instead of cut out a section and replace it you run the risk of the sheet metal blowing out because of the rust between the trunk sheet metal and the tube, especially if the trunk sheet metal is thinned out from the rust.
The other thing you could do is get an HD washer with an internal diameter similar to the outside of the tube diameter. Then use a hole saw to drill out the sheet metal in the trunk, and then slide the HD washer over the end of the tube and weld it into the tube and the trunk as your replacement sheet metal/ tube support. Easier than making a patch, but fresh metal so easier to weld and much less risk of blow outs.