Different Scales for different 4K and FHD displays, in X11 and Wayland

I want to configure different scales for my 4K monitor and the FHD, but it looks an impossible challenge.

Next my different tests and conclusions. A lot of things are not working, so I need to know (to decide) what to try to fix first.

Could you advise me about which path to take to get it working?

One important note: 30Hz is not enough refresh ratio. After a few hours, my eyes are killing me.

Conclusion.

• BUG? Thunderbolt 3 cannot handle 4K higher than 30Hz.
• BUG? HDMI is not working in Wayland. The monitor detects the connection but goes to sleep mode (No signal. Entering in power saving mode).
• BUG? In X11 the Scale option is shared between all displays.
• Fact: Display management is the worst parts of Linux.

Specs.

• SO -> Ubuntu 18.04.2 LTS
• Kernel -> 4.18.0-16-generic
• Drivers -> Nvidia 390.116
• Laptop -> Dell G5 15
• 4K -> LG27UD68P-B
• FHD -> HP 2311x
• Video -> GeForce GTX 1060 with Max-Q Design/PCIe/SSE2
• Video lspci -> NVIDIA Corporation GP106M [GeForce GTX 1060 Mobile]
• Thunderbolt 3 -> Intel Corporation JHL6340
• Thunderbolt 3 to HDMI adapter -> https://www.amazon.com/Cable-Matters-Multiport-Adapter-Ethernet/dp/B01M0K0DL2

Test 1

• X11
• 1 shared Scale option

| Connector   | Display   | Resolution | Hz  |
| ----------- | --------- | ---------- | --- |
| Built-in    | Built-in  | 1920x1080  | 120 |
| HDMI        | 4K        | 3840x2160  | 60  |
| Thunderbolt | FHD       | 1920x1080  | 60  |

Test 2

• X11
• 1 shared Scale option

| Connector   | Display   | Resolution | Hz  |
| ----------- | --------- | ---------- | --- |
| Built-in    | Built-in  | 1920x1080  | 120 |
| HDMI        | FHD       | 1920x1080  | 60  |
| Thunderbolt | 4K        | 3840x2160  | 30  |

Test 3

• Wayland
• HDMI does not work
• 2 shared Scale options

| Connector   | Display   | Resolution | Hz  |
| ----------- | --------- | ---------- | --- |
| Built-in    | Built-in  | 1920x1080  | 60  |
| HDMI        | NO SIGNAL |            |     |
| Thunderbolt | FHD       | 1920x1080  | 60  |

Test 4

• Wayland
• HDMI does not work
• 2 shared Scale options but 4K is not scaling :)

| Connector   | Display   | Resolution | Hz  |
| ----------- | --------- | ---------- | --- |
| Built-in    | Built-in  | 1920x1080  | 60  |
| HDMI        | NO SIGNAL |            |     |
| Thunderbolt | 4K        | 3840x2160  | 30  |