I've found the solution thanks. Just had to keep downloading the installer until Unconfirmed #####.crdownload stopped showing in the downloads folder. Found it strange that on the browser it shows as a finished download.
forge-1.16.5-36.1.0-installer.jar- I've used this to install forge but it does not work and shows me Error: Invalid or Corrupt jarfile
I've tried it with every other forge version (1.16.*, 1.8.*) But the same thing shows.
Please help I've tried reinstalling java over a few times (uninstalling it too)
Jarfix does not work
I've installed them from this webpage in "files"