From: Ron via talk <talk@gtalug.org>
MSI Radeon RX 570 Armor 8G OC
Output: DisplayPort x 3 / HDMI™ / DL-DVI-D
DP Ports: 3x DP v1.4
Are those DP or Mini DP sockets? For some reason, I found more active Mini DP to HDMI than normal DP to HDMI. Searching on AliExpress is a travesty so my data might be bad. Here's one that might work. $13.58 (free shipping; tax unlikely) "Active Mini DisplayPort MiniDP to DVI Adapter Converter multi-screen Eyefinity adapter cable" <https://www.aliexpress.com/item/32621605064.html> Another theory: maybe there are Apple devices with Mini DP non-DP++ ports. Example:
From a tile that said: DP HDMI compatible | Ultra HD 4k | HDMI compatibe Support: AMD Eyefinity Multi-Dispaly Technology 4K * 2K | Mini DP >>> HDMI-compatible
<https://www.aliexpress.com/item/1005006224629754.html> The "title" is "1.8M Mini DP Display Port Thunderbolt 2 To HDMI-compatible Cable Pro Adapter Plated Gold for Macbook Mini IMac" This is definintely for Mac. It implies that the Mac mini DP port is somehow Thunderbolt 2. It doesn't mention Eyefinity. It seems too cheap to be active.
So, I guess no mention of DP++, and since there's already a DVI, no need from their point of view.
That sounds like the problem. Seems pretty dumb, unfortunate, and surprising.