I have similar issue, the resolution of my monitor is 2560x1440. The system logs are as follows:
Apr 21 15:46:49 r6c kernel: [ 6.648224] rockchip-system-monitor rockchip-system-monitor: system monitor probe
Apr 21 15:46:49 r6c kernel: [ 6.648940] Serial: 8250/16550 driver, 10 ports, IRQ sharing disabled
Apr 21 15:46:49 r6c kernel: [ 6.650007] random: fast init done
Apr 21 15:46:49 r6c kernel: [ 6.650059] random: crng init done
Apr 21 15:46:49 r6c kernel: [ 6.650950] rockchip-vop2 fdd90000.vop: Adding to iommu group 14
Apr 21 15:46:49 r6c kernel: [ 6.656798] rockchip-vop2 fdd90000.vop: [drm:vop2_bind] vp0 assign plane mask: 0x285, primary plane phy id: 2
Apr 21 15:46:49 r6c kernel: [ 6.656807] rockchip-vop2 fdd90000.vop: [drm:vop2_bind] vp1 assign plane mask: 0xa, primary plane phy id: 3
Apr 21 15:46:49 r6c kernel: [ 6.656825] rockchip-vop2 fdd90000.vop: [drm:vop2_bind] vp2 assign plane mask: 0x140, primary plane phy id: 8
Apr 21 15:46:49 r6c systemd[1]: Starting Create Volatile Files and Directories...
Apr 21 15:46:49 r6c kernel: [ 6.656833] rockchip-vop2 fdd90000.vop: [drm:vop2_bind] vp3 assign plane mask: 0x0, primary plane phy id: -1
Apr 21 15:46:49 r6c kernel: [ 6.656838] rockchip-drm display-subsystem: failed to get hdmi0_phy_pll: -2
Apr 21 15:46:49 r6c kernel: [ 6.656843] rockchip-drm display-subsystem: failed to get hdmi1_phy_pll: -2
Apr 21 15:46:49 r6c kernel: [ 6.656916] rockchip-vop2 fdd90000.vop: [drm:vop2_bind] Esmart3-win0 as cursor plane for vp0
Apr 21 15:46:49 r6c kernel: [ 6.668177] rockchip-drm display-subsystem: bound fdd90000.vop (ops 0xffffffc0111bdc00)
Apr 21 15:46:49 r6c kernel: [ 6.668855] dwhdmi-rockchip fde80000.hdmi: registered ddc I2C bus driver
Apr 21 15:46:49 r6c kernel: [ 6.669007] rockchip-drm display-subsystem: bound fde80000.hdmi (ops 0xffffffc0111c6410)
Apr 21 15:46:49 r6c kernel: [ 6.669357] rockchip-drm display-subsystem: failed to parse loader memory
Apr 21 15:46:49 r6c kernel: [ 6.887021] dwhdmi-rockchip fde80000.hdmi: use tmds mode
Apr 21 15:46:49 r6c kernel: [ 6.887072] rockchip-vop2 fdd90000.vop: [drm:vop2_crtc_atomic_enable] Update mode to 1920x1080p60, type: 11(if:800) for vp0 dclk: 148500000
Apr 21 15:46:49 r6c kernel: [ 6.887227] rockchip-vop2 fdd90000.vop: [drm:vop2_crtc_atomic_enable] dclk_out0 div: 0 dclk_core0 div: 2
Apr 21 15:46:49 r6c kernel: [ 6.887238] rockchip-vop2 fdd90000.vop: [drm:vop2_crtc_atomic_enable] set dclk_vop0 to 148500000, get 148500000
Apr 21 15:46:49 r6c kernel: [ 6.887271] rockchip-hdptx-phy-hdmi fed60000.hdmiphy: hdptx_ropll_cmn_config bus_width:16a8c8 rate:1485000
Apr 21 15:46:49 r6c kernel: [ 6.887549] rockchip-hdptx-phy-hdmi fed60000.hdmiphy: hdptx phy pll locked!
Apr 21 15:46:49 r6c kernel: [ 6.887552] dwhdmi-rockchip fde80000.hdmi: final tmdsclk = 148500000
Apr 21 15:46:49 r6c kernel: [ 6.887582] dwhdmi-rockchip fde80000.hdmi: don't use dsc mode
Apr 21 15:46:49 r6c kernel: [ 6.887585] dwhdmi-rockchip fde80000.hdmi: dw hdmi qp use tmds mode
Apr 21 15:46:49 r6c systemd-tmpfiles[710]: Setting file flags is only supported on regular files and directories, cannot set on '/var/log/journal'.
Apr 21 15:46:49 r6c kernel: [ 6.887592] rockchip-hdptx-phy-hdmi fed60000.hdmiphy: bus_width:0x16a8c8,bit_rate:1485000
Apr 21 15:46:49 r6c kernel: [ 6.887785] rockchip-hdptx-phy-hdmi fed60000.hdmiphy: hdptx phy lane locked!
Apr 21 15:46:49 r6c kernel: [ 6.954037] dwhdmi-rockchip fde80000.hdmi: use tmds mode
Apr 21 15:46:49 r6c kernel: [ 6.970706] Console: switching to colour frame buffer device 240x67
Apr 21 15:46:49 r6c kernel: [ 6.970810] dwhdmi-rockchip fde80000.hdmi: use tmds mode
Apr 21 15:46:49 r6c kernel: [ 7.017772] rockchip-drm display-subsystem: [drm] fb0: rockchipdrmfb frame buffer device
