mint is trying open the .run file as a graphical image.
Right click on the file, select Properties / Permissions, set it as executable and try double clicking again.
Or,
Open a terminal, cd to Downloads, and enter:
chmod +x qcad-3.24.3-trial-linux-x86_64.run
then run it with:
./qcad-3.24.3-trial-linux-x86_64.run
Dave