MacOsX - Graphic Slowdown in Legion Content

I am running WoW on a iMac 5k 2017 on Ultra settings, and both outside and inside raids everything runs smoothly at 50/60fps. In fact I was surprised to see how better the game runs with the latest upgrades in software both from Blizzard and Apple.

However, I recently decided to finish some old Legion content, Class Campaigns and the like… and everytime I move to the Broken Isles and related areas, the graphics slow down to 20fps.

Is there any known reasons for it? Admittedly it is not a big issue since it’s not new content, but I am curious as to why it might be doing it.

Out of your topic, do you run the game in low resolution mode or 5K resolution with 50% scale?

I am using ElvUI so not exactly sure.

It defaults to 5k resolution, 50% scale and setting 5.
I think the new expansion was designed to be less demanding.
Val’Sharah in particular, with all the trees, is a bit too much for the imac.
Also my imac started to throttle at some point which doesn’t help.
You can check whether it does that if you use intel power gadget, from intels website.

Val’Sharah looks neat. Actually, the overall expansion looks decent. I love to quest there.

As you mentioned it is a highly demand area. my iMac 2019 barely reach 60 FPS. I max out all graphic settings.