When the cursor in next to a parenthesis, bracket, or brace, it highlights it and the matching one (if any). This is expected.
But by "highlights", I mean it entirely hides the things under a small block of color that nearly matches the text, making it impossible to read which kind of symbol it is. Is there a way to change this highlight style to a border-like box instead?
Here's a screenshot of my issue:
If you don't want such highlighting at all then turn off show-paren-mode.
If you do want it, but you want it to use a different color:
Put your cursor on that highlighted text and hit C-u C-x =. Near the bottom of buffer *Help* it tells you what face is used for the highlighting.
M-x customize-face and enter that face. Then change its attributes (e.g. foreground, background colors) as you like. Then save your changes.
face text property on the character that you asked about in that image. You do not see face listed with the text properties, along with property fontified. You need to put the cursor just before (a block cursor will appear to be on top of) the parenthesis character, and then hit C-u C-x =.
Box around text works for me. But it can depend on your platform, the font used, etc. Try customizing some other face, which is used more generally (not just for parens), setting, say Box around text with Width 2, Color Red, and Style None, to see whether that works. If it doesn't then try changing the font of the face. IOW, experiment, starting with checking whether it works at all with your setup. And start with emacs -Q, to be sure that something in your init file is not interfering.