Comment 7 for bug 1890418

Actually the problem might just be that the Linux kernel doesn't understand extended vendor-specific display timings. I've decoded your monitor's EDID and it reveals that 3840x2160 30Hz is mentioned:

edid-decode (hex):

00 ff ff ff ff ff ff 00 04 69 a3 28 24 51 00 00
0e 1b 01 03 80 3e 22 78 3a 1c b5 a3 57 4f a0 27
0d 50 54 bf ef 00 d1 c0 81 40 81 80 95 00 b3 00
71 4f 81 c0 01 01 04 74 00 30 f2 70 5a 80 b0 58
8a 00 6d 55 21 00 00 1a 02 3a 80 18 71 38 2d 40
58 2c 45 00 6d 55 21 00 00 1e 00 00 00 fd 00 1e
50 18 a0 1e 00 0a 20 20 20 20 20 20 00 00 00 fc
00 41 53 55 53 20 50 42 32 38 37 51 0a 20 01 83

02 03 2c f1 51 01 02 03 11 12 13 04 14 05 0e 0f
1d 1e 1f 90 20 22 23 09 17 07 83 01 00 00 6d 03
0c 00 20 00 00 3c 20 00 60 01 02 03 56 5e 00 a0
a0 a0 29 50 30 20 35 00 6d 55 21 00 00 1e e2 68
00 a0 a0 40 2e 60 30 20 36 00 6d 55 21 00 00 1a
01 1d 00 bc 52 d0 1e 20 b8 28 55 40 6d 55 21 00
00 1e 8c 0a d0 90 20 40 31 20 0c 40 55 00 6d 55
21 00 00 18 00 00 00 00 00 00 00 00 00 00 00 5e

----------------

EDID version: 1.3
Manufacturer: ACI Model 10403 Serial Number 20772
Made in week 14 of 2017
Digital display
Maximum image size: 62 cm x 34 cm
Gamma: 2.20
DPMS levels: Off
Undefined display color type
First detailed timing is preferred timing
Color Characteristics
  Red: 0.6367, 0.3408
  Green: 0.3115, 0.6250
  Blue: 0.1542, 0.0537
  White: 0.3134, 0.3291
Established Timings I & II
    720x400 70.082 Hz 9:5 31.467 kHz 28.320 MHz (IBM)
    640x480 59.940 Hz 4:3 31.469 kHz 25.175 MHz (DMT)
    640x480 66.667 Hz 4:3 35.000 kHz 30.240 MHz (Apple)
    640x480 72.809 Hz 4:3 37.861 kHz 31.500 MHz (DMT)
    640x480 75.000 Hz 4:3 37.500 kHz 31.500 MHz (DMT)
    800x600 56.250 Hz 4:3 35.156 kHz 36.000 MHz (DMT)
    800x600 60.317 Hz 4:3 37.879 kHz 40.000 MHz (DMT)
    800x600 72.188 Hz 4:3 48.077 kHz 50.000 MHz (DMT)
    800x600 75.000 Hz 4:3 46.875 kHz 49.500 MHz (DMT)
    832x624 74.551 Hz 4:3 49.726 kHz 57.284 MHz (Apple)
   1024x768 60.004 Hz 4:3 48.363 kHz 65.000 MHz (DMT)
   1024x768 70.069 Hz 4:3 56.476 kHz 75.000 MHz (DMT)
   1024x768 75.029 Hz 4:3 60.023 kHz 78.750 MHz (DMT)
   1280x1024 75.025 Hz 5:4 79.976 kHz 135.000 MHz (DMT)
Standard Timings
   1920x1080 60.000 Hz 16:9 67.500 kHz 148.500 MHz (DMT)
   1280x960 60.000 Hz 4:3 60.000 kHz 108.000 MHz (DMT)
   1280x1024 60.020 Hz 5:4 63.981 kHz 108.000 MHz (DMT)
   1440x900 59.887 Hz 16:10 55.935 kHz 106.500 MHz (DMT)
   1680x1050 59.954 Hz 16:10 65.290 kHz 146.250 MHz (DMT)
   1152x864 75.000 Hz 4:3 67.500 kHz 108.000 MHz (DMT)
   1280x720 60.000 Hz 16:9 45.000 kHz 74.250 MHz (DMT)
Detailed mode: Clock 297.000 MHz, 621 mm x 341 mm
               3840 4016 4104 4400 (176 88 296)
               2160 2168 2178 2250 ( 8 10 72)
               +hsync -vsync
               VertFreq: 30.000 Hz, HorFreq: 67.500 kHz
Detailed mode: Clock 148.500 MHz, 621 mm x 341 mm
               1920 2008 2052 2200 ( 88 44 148)
               1080 1084 1089 1125 ( 4 5 36)
               +hsync +vsync
               VertFreq: 60.000 Hz, HorFreq: 67.500 kHz
Display Range Limits
  Monitor ranges (GTF): 30-80 Hz V, 24-160 kHz H, max dotclock 300 MHz
Display Product Name: ASUS PB287Q
Has 1 extension block
Checksum: 0x83

----------------

CTA-861 Extension Block Revision 3
Underscans PC formats by default
Basic audio support
Supports YCbCr 4:4:4
Supports YCbCr 4:2:2
1 native detailed modes
40 bytes of CTA data blocks
  Video Data Block
      640x480 59.940 Hz 4:3 31.469 kHz 25.175 MHz (VIC 1)
      720x480 59.940 Hz 4:3 31.469 kHz 27.000 MHz (VIC 2)
      720x480 59.940 Hz 16:9 31.469 kHz 27.000 MHz (VIC 3)
      720x576 50.000 Hz 4:3 31.250 kHz 27.000 MHz (VIC 17)
      720x576 50.000 Hz 16:9 31.250 kHz 27.000 MHz (VIC 18)
     1280x720 50.000 Hz 16:9 37.500 kHz 74.250 MHz (VIC 19)
     1280x720 60.000 Hz 16:9 45.000 kHz 74.250 MHz (VIC 4)
     1920x1080i 50.000 Hz 16:9 28.125 kHz 74.250 MHz (VIC 20)
     1920x1080i 60.000 Hz 16:9 33.750 kHz 74.250 MHz (VIC 5)
     1440x480 59.940 Hz 4:3 31.469 kHz 54.000 MHz (VIC 14)
     1440x480 59.940 Hz 16:9 31.469 kHz 54.000 MHz (VIC 15)
     1440x576 50.000 Hz 4:3 31.250 kHz 54.000 MHz (VIC 29)
     1440x576 50.000 Hz 16:9 31.250 kHz 54.000 MHz (VIC 30)
     1920x1080 50.000 Hz 16:9 56.250 kHz 148.500 MHz (VIC 31)
     1920x1080 60.000 Hz 16:9 67.500 kHz 148.500 MHz (VIC 16, native)
     1920x1080 24.000 Hz 16:9 27.000 kHz 74.250 MHz (VIC 32)
     1920x1080 30.000 Hz 16:9 33.750 kHz 74.250 MHz (VIC 34)
  Audio Data Block
    Linear PCM, max channels 2
      Supported sample rates (kHz): 96 48 44.1 32
      Supported sample sizes (bits): 24 20 16
  Speaker Allocation Data Block
    Speaker map:
      FL/FR - Front Left/Right
  Vendor-Specific Data Block, OUI 0x000c03 (HDMI)
    Source physical address 2.0.0.0
    Maximum TMDS clock: 300 MHz
    Extended HDMI video details:
      HDMI VICs:
         3840x2160 30.000 Hz 16:9 67.500 kHz 297.000 MHz (HDMI VIC 1)
         3840x2160 25.000 Hz 16:9 56.250 kHz 297.000 MHz (HDMI VIC 2)
         3840x2160 24.000 Hz 16:9 54.000 kHz 297.000 MHz (HDMI VIC 3)
Detailed mode: Clock 241.500 MHz, 621 mm x 341 mm
               2560 2608 2640 2720 ( 48 32 80)
               1440 1443 1448 1481 ( 3 5 33)
               +hsync +vsync
               VertFreq: 59.951 Hz, HorFreq: 88.787 kHz
Detailed mode: Clock 268.500 MHz, 621 mm x 341 mm
               2560 2608 2640 2720 ( 48 32 80)
               1600 1603 1609 1646 ( 3 6 37)
               +hsync -vsync
               VertFreq: 59.972 Hz, HorFreq: 98.713 kHz
Detailed mode: Clock 74.250 MHz, 621 mm x 341 mm
               1280 1720 1760 1980 (440 40 220)
                720 725 730 750 ( 5 5 20)
               +hsync +vsync
               VertFreq: 50.000 Hz, HorFreq: 37.500 kHz
Detailed mode: Clock 27.000 MHz, 621 mm x 341 mm
                720 732 796 864 ( 12 64 68)
                576 581 586 625 ( 5 5 39)
               -hsync -vsync
               VertFreq: 50.000 Hz, HorFreq: 31.250 kHz
Checksum: 0x5e