Eyebrows tend to change over time. Some get super bushy; some fade away. I was going to ask if there were ever any CAS sliders made for the density of eyebrows, but the more I thought about it, the less sense that made. So what I'd like to find are some downloadable eyebrow styles, that would give the appearance of faded brows, a sort of "peach fuzz" if you will. I tried just canceling the brows altogether (in the makeup & facial hair tab), which wasn't bad on Sims with bangs, but looked a bit alien otherwise. I'd like to be able to see where the eyebrows would be, but just have them be more... transparent, I guess. Morse's Sgt. Lewis, at right in the screenshot, has eyebrows, but compared to Morse's they are much less noticeable.

Density, no - thickness, yes. Nopke's "20 Sliders" include options for making eyebrows thicker or thinner, in whole or in part: https://modthesims.info/d/593107/20-sliders.html
It's also worth noting that when you Change Appearance, you can change eyebrow color separately from hair color (I discovered this recently). If you want eyebrows to be fainter, select a lighter color (blond eyebrows tend to be rather faint) - and of course the converse if you want them more noticeable (the Legolas Effect).

There are also many many eyebrow sets on MTS, some of which may be what you are looking for.

the “Legolas effect”. Yeah, I sort of figured that would be the case. Given the nearly total disregard for thinning hair in general in the simming world, I have a sneaking suspicion that nobody’s going to have thought vanishing eyebrows was something interesting enough to create, but I’ll check out the options on MTS anyway. And obviously, if anyone knows of off-site treasures, the more the merrier. Thanks!

Well, I take it back - there’s certainly not many.., but a handful here on MTS look promising. The “Spring Eyebrows” by Primera are lightweight-ish, at least in the preview pics.

Always search here before you make a WCIF lol.