ZXP Installer extension not compatible/not responding

This is probably a really common question, and trust me I've tried so many solutions. Nothing worked. I'm trying to download the RTFX plugin while using the ZXP Installer. I was using the grey one, I think the one that's not updated and when I open it, it just stays on the grey screen, it never lets me in. So, I decided to get the most recent one, the one with the icon has the red box (ZXPInstaller), and that didn't work either because when I put in the zxp file, it just said that it wasn't compatible. I saw a solution for this on youtube, did not work for me and I saw the same problem on this website but it just led me back to the original one I used 😐. Is there any other solutions or another way I can download RTFX?