Thank you. That seemed to help, although it wasn't straightforward. I didn't download MBST again as it seemed to be the same version as the one I downloaded from @1PW's answer. So I just went to Advanced, and then Clean.
While it was working, a popup came up that Malwarebytes could not be uninstalled. When I closed that, a while later, MBST said it removed it successfully. Then it asked to install the latest version of Malwarebytes, which I confirmed.
It said it was able to install it properly, but a few seconds after, I got a generic-looking Windows popup that said Malwarebytes could be installed properly. In my desktop, the Malwarebytes shortcut icon looked like the generic shortcut icon Windows uses when it couldn't find the app it was connected to.
So I ran MBST to Clean again. This time, it removed it with no problem, after which, I confirmed reinstallation. When it finished, it had the generic-looking Windows popup that said Malwarebytes could be installed properly again. But this time, the shortcut icon in the desktop looked correct. I took a peek at the MBST Clean log, and you will see that it says the installation was aborted at the very end.
A few seconds later, Malwarebytes actually opened on its own. I restarted the computer, and after that, I ran Malwarebytes to scan. It was able to do that and it detected no threats.
mbst-clean-results.txt