I haven't understood if I can use my 5 xilinx xcs20 with one of those bitstream for something miner related or I will have to sell them
If I have found the documentation for the correct XCS20 (
https://www.xilinx.com/support/documentation/data_sheets/ds060.pdf ) then I very much doubt that you would be able to use them for mining since they have only 950 logic cells.
They were also end-of-lifed several years ago.