Similar question to Visual Studio 2022: How to remove highlighting from block sections, but here's how I was able to solve it somewhat.

I am using Visual Studio Community 2022 v17.13.6 and was able to mostly get rid of this by going to Tools > Options > Environment > Fonts and Colors. In the "Show setting for" select "Text Editor". I set "Highlighted Reference" Item background to the same as my "Plain Text" Item background color. There is still a box around them, but it makes it much easier to see. There is also an option called "Highlighted Definition" with the same settings, but I don't know when that is used so I left it as is.