I've run into this frustrating glitch more than once. I've tried 4.20.1, 4.21.1, I tried the old zip you linked.
No matter what I do, fresh install, old install, any version now, the screen magnifies immediately after I tell it to "select a region", OR, if I simply hit the print-screen button to capture the entire screen, it captures a zoomed image.
I'm running Windows 10 Pro 64-bit, a single monitor (65" screen). The computer DOES have to use AMD's Radeon scaling ability to scale the screen SMALLER since the graphics card wants to make the image larger than the 1920x1080p borders for some reason. So AMD software changes the "HDMI Scaling" by 6 percent in order to shrink the image to fit the 65" tv.
With that said, I've been using this Screenshot Captor software for a couple years now. And the software worked GREAT until the recent SC update. After that, it just started auto-zooming all the time, and I can't seem to find a version that DOESN'T do it now.
EDIT!!! I'm a computer technician... but my brain was really not working earlier (apparently). I realized that if NONE of your versions of software worked properly, then it wasn't SC that changed, it was something else. And since we're talking about AMD Scaling issues or 'scaling' issues in almost every situation , I uninstalled my AMD video drivers and reinstalled them. The issue was caused by AMD's own drivers interacting with SC somehow causing the magnification. After driving re-install, works perfectly again.