High Quality Display is slow with rainbow beachball

Are there any InDesign users out there using an eGPU on a Mac to accelerate display performance?

I use Adobe InDesign quite a bit and I would like to see better performance in the "High Quality Display" mode. In medium to very complex documents I see a lot of rainbow beachball while it tries to redraw the document. It's interesting in that I get great performance in Photoshop and Illustrator, but InDesign seems fussy about it.

Would an eGPU help with this? Which one should I consider? Or is an eGPU only for 3D and video?

I am running InDesign 15.0.1 on an iMac 2018 with 32 G RAM and 3.2 GHz 6-Core Intel Core i7 - what the heck kind of beastly machine gets good performance in the High Quality Display mode?