Transmission fluid crash course needed pronto.

So there's mixed opinions on what goes on, and there's a few different things going on, one problem is if you change the fluid too often, one is if you change it too infrequently.

1. A transmission that hasn't had the fluid changed often enough will end up with a lot of wear metals in it, particularly from clutch plates, for the same reason that not changing your oil will do that, but draining that out can actually be bad for a transmission, because the wear metals were increasing the friction to make up for the worn out contact surfaces but now they've been drained out, so it may start to slip when it tries to shift. CVTs don't quite have discrete shift points, but they do have a valve body and a clutch, so I imagine the same concept applies, but it might actually be worse as they're basically doing smooth constant shifting throughout their operation, and friction is somewhat important for their operation as they don't use "gears" when shifting, they use a belt being compressed by the edges of two conical gears.
2. Some of those wear metals might clump up together in a part of the valve body, then the addition of the new fluid might loosen them up and cause them to float down the valve body to a different spot and possibly cause a clog, kinda like when a person has a stroke. A valve body having a clog in the wrong spot can cause anything from slight weirdness or shift delays, to the transmission grenading itself because something didn't move when it should have, or moved when it shouldn't have, and two parts that shouldn't collide have collided and tore each other to shreds.

Bonus concern: Having the transmission connected to a flushing machine and having clean fluid rammed in one side and dirty fluid forced out the other might possibly cause this same clumping in the valve body, especially if the flush machine was not cleaned out before use - you might get some other car's dirty fluid getting crammed into your transmission, so a "flush" is generally discouraged these days in favor of a simple drain and fill.

There is a LOT of debate on how likely or how important each phenomenon is, but basically Toyota technicians are trained to either never do a transmission fluid change, or to offer to do a drain and fill once every 60k mi at most. The whole transmission and torque converter can contain up to 15 quarts of fluid, but a simple drain and fill only replaces a small fraction of that, maybe 3 to 5 or so depending on model. I suppose the idea is that adding a little new fluid freshens it up and restores the lubrication properties without removing a lot of the wear metals, but also doing this fairly often prevents a lot of wear in the first place, so the perceived difference in shifting performance between one flush and the next would theoretically be minimal. To me it sounds like this guidance is designed as a sort of middle of the road compromise. I think the above concerns really only matter if you (or a previous owner) have ever gone too long without a drain and fill, because the older and dirtier and more worn out that the fluid gets, the more that wear increases exponentially, so there's probably no harm in doing a drain and fill too often.

This stuff only applies for CVTs, possibly dual clutch, and regular automatics. Manual transmissions are simpler and can be changed as often as you like with no harm done, and can easily be taken apart and have the clutch packs replaced entirely.

Is it a Hybrid or not? If it's not a hybrid, switch dealerships, they are going to cost you a transmission, which is around $8k plus labor!