I think that the answer to this largely depends on your local market. In most markets, Highlander Hybrids and Grand Highlander Hybrids are in high demand- so they are going for MSRP. In some areas, it seems like dealers are able to add markups or dealer packages to these vehicles as a condition of purchase- and consumers either have to deal with those added costs or go without.
There are five Toyota dealers within 30 minutes of my home- 7 within an hour. Of those, two sell those hybrids for MSRP- but often you need to wait- and the waiting time can vary depending on how picky the buyer is about trim/color/option. The other five all charge either dealer markups or add packages as a condition of purchase- ranging from $895 to $5000. Note- this is in SE Wisconsin.
Non-hybrid variants have a bit more wiggle room in my area. I bought my 2023 Highlander Platinum in June and was able to get $3000 after negotiating and walking away when I didn't originally get the price that I wanted. FWD base Highlanders are being advertised in my area for $2500ish off of MSRP. The only hybrid models in my area that seem to be selling below MSRP in my area seem to be the Highlander Bronze Edition. People buy up LE, XLE, Limited, and Platinums and those are in strong demand. For some reason, it can take a while for the Bronze Hybrid models to sell. Sometimes they sell for MSRP before they arrive on the lot- other times, you can see it on the dealer's website as "incoming"... and it isn't marked as "sale pending"... and then it gets updated to "on the lot"... and after a week or so it gets a $500 discount, then $1000 after about two weeks... most move at that point if they haven't been sold at the $500 discount.
Discounts on non-hybrid Grand Highlanders is spotty in my neck of the woods. Limited and Platinums don't seem to have much wiggle room, while XLEs seem to stay on the lot for a while longer- resulting in slight discounts from some dealers.
The best move is for you to really examine the market in your area. Start watching the websites at your local dealerships... and watch how long the vehicles that you are interested in stay listed before being sold. If the turnaround is quick- then there's probably not much wiggle room. If you notice cars that are listed- and they stay listed for a while- and then you spot one or two that come close to what you want- start reaching out to those dealers.
If your market is rough in terms of discounts and/or availability- perhaps looking a bit outside of your local market.