Microsoft Word Theme changes actual font colours

So I discovered that since upgrading to Windows 11, all of my document formatting was messed up. Namely, the outline colour I used on some titles and whatnot was yellow. No matter which colour I changed to, it was yellow. I contacted support about this issue (which is the single most frustrating thing in the world) and they remoted to my PC. After trying all kinds of things, Santiago Jr changed the theme of Word. I use "dark" because the standard white screen messes with my eyes while typing.

That resolved the issue! Excellent. Except it makes zero sense that a theme would change the actual outline colour. See, I saved my document as a PDF to see if the yellow was "part of the theme" or actual colour (i.e. what it would print like) and the yellow was actual colour. Change the theme, and I can have any colour I want as the outline. Change it back, and outlines are always yellow.

Might seem like the issue is resolved, except WHY is the actual colour of an outline linked to the view theme? If I film a video while wearing sunglasses, the video doesn't come out darker.

Oh and Mr Santiago Jr closed the chat, disconnected remote access, and marked the ticket as resolved without actually checking it had been resolved. In fact, I had sent a message saying "this hasn't fixed it" before he signed off. But the absolute lack of customer support I get from Microsoft isn't the issue here, the fact that changing the theme in Word somehow changes the actual colours of the document.

So here I am, unwilling to deal with so-called "support" again because they're useless, and hoping someone on here might have an answer. Or at least know how to raise the issue with someone who isn't useless.