What about light intensity, air humidity and temperature on the windowsill? And how does the plant look from bottom? I think it might be a case of overheat or serious underwatering. We have extra hot and dry summer here and I water my xerographica every day - misting whole plant + letting some water in the middle.

The window has been open and it's pretty humid here in Illinois as of late but it's also sitting in air conditioning some days. The window faces east so it gets some morning sunlight but there are quite a few large trees in the way. Here's a picture of the bottom. Nothing feels mushy so that's why I'm not really thinking rot.

Try to water it properly every day then.

Hi sorry for the late response but I was out of town. I had watered it before I left and then I just watered it again but it's still looking pretty brown :/ could it be dry rot?

Rot doesn't start in the middle of top leaf. I really think it's underwatering. Or maybe something temperature related. Once leaves are damaged, they won't heal - you can trim completely dry ones later.
Be sure you give adequate amount of water to your plant. If it's really hot, water it every day (misting or dunking for 5 seconds is enough). If weather goes bad, water it less.
T. xerographica is big plant, but grows relatively slowly, so it will take a lot of time to see any changes.

I just reread Today2 saying "but it's still looking pretty brown :/ could it be dry rot?" with a picture of the root area, but that area looks fine to me, looks like my two plants, which are hanging out in a north-facing porch (lots of reflected light) and I soak them for an hour or so once a week (we have very dry air unless it's raining, which isn't often).

Thank you all for your help! I will give it more baths now in hopes that it starts to perk up a little :)