Why do you say eGPU isn't a good option? I'm curious because I'm tempted to get an eGPU to accelerate all the image editing that I need to do.
I owned the Sonnet eGFX Breakaway Box 550, and used a Gigabyte Radeon RX VEGA 56 Gaming OC 8GB in it.
This card has noticeably better cooling and a quiet fan profile for more silent operation than the reference Vega 56 cards.
Still, though, this was an extremely noisy setup. Having a eGPU box on your desk will be quite audible. The fans from the GPU and the power supply in the eGPU box is gonna be very noticeable since the box sits on your desk. The egpu boxes are not sound dampened at all.
Traditional computer cases were usually more sound dampened, and they also usually sat under your desk, not on it. Also, tradition computer cases has significantly better airflow and access to air than these egpu boxes has, so the fans don't have to spin as fast.
I would only consider a watercooled eGPU solution if I was ever gonna try it again.
Also, some games and apps simply didn't work well with the eGPU. Even in High Sierra 10.13.5. And that includes Apple's own Final Cut Pro X 10.4, which doesn't even use the performance of the eGPU AT ALL. FCPX only uses the eGPU for live rendering, but not for exporting, transcoding, or any of the really heavy media tasks... So what's the point.