I've been trying to export an HD video from a screen recording created with Camtasia studio, but every rendering is returning videos with 80 mb/s of bitrate, I'm setting it to 65% quality, MP4. If I change to bitrate, let's say I set 6000, the file output is way smaller, but the quality is terrible, like you can't see a thing in the video. I've even tried compression with AVI, same results. I've also tried converting the video with other software, even online software, same thing. I also decreased the quality from 65% to 33%, same bad result. I don't know why Camtasia puts so much much bitrate into a single file. I even tried exporting as WMV, again, same thing. It's a 50 seconds video, it has 850 mb of file size.
The filesize is determined by many factors. First, check your resolution. If you're exporting in 4k or 6k, your filesize might not be strange at all. Next, the framerate plays a big part in filesizes aswell. Check if you're exporting in 30fps (for most web-videos), 25fps (for tv) or 24fps (for cinema). It might just be that you are using something like 60 or 120fps, which bloats the file. Next up is the codec and container you are using. You mentioned trying the .avi and .mp4 container, but which codec were you using? For .mp4 files I recommend h.264 or h.265, which are the most common codecs for mp4.