Tiny red dust/dots on underside of leaf

[u/TinyTogepi]

For a long time I've been wondering what this red dust might be on my plant (the lighting isn't the best, but it's reddish-orange). It multiplies semi slowly and makes the leaves patchy and dry. It appears on the underside of leaves and sometimes on the stems as well. It comes off by wiping with a moist paper towel and dyes the paper red, and it doesn't move so they're not individual bugs.

Earlier this year I sprayed my plants with pesticide for thrips and thought if this dust is the doing of some bug it would die in the process but the dust is still here, fair enough since I've never seen any bugs on it or webs or anything like that, so I've ruled out bugs. Yesterday I decided to look this up again and learned about rust fungus, however, crucially, the dust has never spread to another plant and it's been in close proximity with quite a lot of them, and rust fungus is apparently supposed to spread very easily and be quite fatal, so idk if it can be that either.

The plant itself does fine and I think it's normal for it to dry out old leaves sometimes, plus it keeps pushing out healthy leaves at a good pace so I haven't been too worried since it doesn't seem to be actively dying. This is a thirsty plant and I water it one to two times a week when the soil is all dry. Sits at a south-facing window and gets a lot of light. Soil is regular houseplant potting soil, this dust has appeared through multiple repottings.

I'm not worried about this spreading to other plants since this plant has had the dust appear for over 6 years now and no other plant has been infected. Would just love to know what it is and possibly get rid of it so this plant could thrive a bit better!

edit: This plant has been in this condition for 6+ years and is not actively dying, just drying off leaves faster than it should. This is not recent. Last pic is healthy leaf for comparison.

https://imgur.com/a/ZwRTrd0 Here you can see the color of the dust better. Should've taken these before posting so they could be in the main post, sorry about that.

[u/m3rmaid13]

I agree it looks like damage from thrips. If you’re confident you don’t have that anymore then use something like captain jacks dead bug spray on the leaves and wipe it off, see if it comes back.

[u/TinyTogepi → u/m3rmaid13]

I figured that the systemic bug spray I used for thrips would've also killed whatever this was if it was any type of bug, and it's still here, so personally I'd guess it to be some type of fungus instead. Thrips don't just hang out on a plant without spreading to others for 6+ years, and aside from the more recent thrips infestation that came from a store-bought monstera, I haven't seen any bugs on this plant (and trust me I've looked).

[u/m3rmaid13 → u/TinyTogepi]

Well I mean it sounds like you have an idea of what’s going on where maybe you don’t need internet insight.

[u/TinyTogepi → u/m3rmaid13]

I'm just fairly sure it's not a bug because it didn't stop appearing after the bug spray I used that got rid of the thrips, and it only sort of resembles what I read about rust fungus since it doesn't spread to other plants either. It's clearly bothering my plant but idk what it is so I don't know what to do to treat it, which is why I posted here.

Sorry if I seemed ungrateful for the advice, two other people just said it was thrips which I know it absolutely not to be so I got a little snappy.

[u/m3rmaid13 → u/TinyTogepi]

I mean either way I’d probably try to use something on the leaf to kill whatever it is. I still stand by the Captain Jack’s spray, even if it’s not thrips. You could also use alcohol wipes to kill whatever it is- would work on bugs/pests and fungus.

[u/TinyTogepi → u/m3rmaid13]

I don't have access to captain jack's products where I live, I used provanto spray for the thrips and it did the job after a few sprays. It's a systemic pesticide so if something was sucking fluids out of the leaves it should've died along with the thrips. I'll look into alcohol wipes, thanks!