Since you're not looking for absolute maximum throughput for your GPU (just driving monitors), a dock with TB3 passthrough for eGPU would basically solve all your issues really easily.
The CalDigit TS3 Plus
DOES offer TB3 passthrough and the Sonnet eGFX 650 OC does work to drive 3 monitors via TB3 downstream with an RX 5700 XT installed. Have tested that exact config on MBP16,1. The issue (for my needs) is it only has 87W PD via single cable.
ALL of the eGPU's with additional functionality built in (USB, ethernet, etc) have flaky support with macOS. Nearly every single review fails to focus on this aspect, except a few that recommend the Razer Core X Chroma for the "better" PSU in macOS. They explicitly note the USB/ethernet is useless in macOS. There are some newer models on the way, but unless they
specifically advertise macOS support for additional port functionality, would not trust without extensive testing.
Sonnet eGFX Breakaway Box 650 OC (GPU-650WOC-TB3) is compatible with RX 5700 XT and using it with MBP16,1 without any physical issues. All issues are with the AMD 5XXX series drivers, mainly with METAL.
Desktop Thunderbolt 3 eGPU adapter box with one PCIe expansion slot for high-performance AMD and NVIDIA gaming video cards, and professional audio, video, fibre, RAID and ethernet PCIe cards.
www.sonnetstore.com
Here's the exact compatibility list that they regularly update with exact vendor part numbers:
If your current GPU is NOT exactly listed on that, there may be an eGPU compatibility issue with macOS. At least worth checking.
Razer does NOT support anything other than their exact list for macOS. Other cards "work" but it's clear they have no intention of really beefing up their macOS offerings. I'd look at Sonnet moving forward. They are making Mac-specific centered products, offering advertised support with newest products and are constantly updating. It's a fresh approach compared to other vendors.
Razer's current GPU list:
AMD Radeon™ RX 580
AMD Radeon™ RX 570
AMD Radeon™ Pro WX 7100
AMD Radeon™ RX Vega 56
AMD Radeon™ RX Vega 64
AMD Vega Frontier Edition Air
AMD Radeon™ Pro WX 9100
AMD Radeon™ RX 470
AMD Radeon™ RX 480