I would only trust what is rated 4K at the pishop usa. Another thought reading you comment is to try boosting the power to your 4k monitor in config.txt. I forgot what exactly the line verbiage would be with out looking it up.
It is reading the EDID info from your monitor. It is grabbing what is considered the default resolution line from the monitor’s edid.
It is not getting any info from you 4K tv monitor. So it is probably falling back to what it considers safe.
Just looked this up (config_hdmi_boost=) and it is not allowed on the pi4.
I am going to have to try adding my own video= parameter, the parameters specified in cmdline.txt come after, it might override.
Well, adding the parameter does override the one that is detected. However I was not able to get a working display. I am now going to switch to the cable that produces 640x480 and see what is detected. The cable is a foot cable from CanaKit.
Well, this is embarrassing. Turns out I have the Argon One case, which has a board to reroute the power and the hdmi ports… I have been using the 2nd video port all along. I noticed when attempting to define the hdmi_mode and group that I noticed the kernel parameters then had a second video parameter.
And sure enough, I moved the cable to the correct video port and presto… 4K via fbturbo. However the v3d driver does not load if I uninstall fbturbo. Xorg just falls back to the fb driver and glxinfo shows llvmpipe with fbturbo installed.
I still need to test this again the 4K TV/monitor on Monday.
So currently I am running sync’ed to arm-unstable with mainline kernel, new bootloaders while running on an SD card. Tomorrow I will try to migrate this an SSD with f2fs compression.
last rc2 kernel & bootloaders and mesa-git.
can not boot with kms, screen rainbow square, only fkms or kms-pi4 boot .
if boot, firefox play youtube flick rainbow.
I can confirm the 4GB RPi boots from SSD and has working keyboard and mouse with both mainline and rc, with the latest bootloaders.
I can also confirm the CanaKit HDMI cable is not compatible with this Dell monitor, they only produce 640x480. If I boot with my UGREEN cable and then switch to the CanaKit cable, it will display 4K, but together they will not boot into 4K. Tested with arm-unstable mainline and rc and with Pi OS 64bit.
@darksky Feel free to delete all of these 4K video related posts. This turned out to be more of a hardware issue and are pretty worthless spam for this thread.
Setting total memory to 4GB in config.txt for an 8GB RPi4
total_mem=4096
had no effect on the booting with SSD and the non-functional mouse and keyboard with the rc2 kernel.
I found this today, seems a fix is on the way.
https://github.com/raspberrypi/linux/commit/2ef5f8f788a8b2511fe7247fb00e1310fb96e1b9
Finally. They for days blew me off and wanted to close my issue. That issue #3747 is mine referenced in the commit. I will build new kernels today.
Well that is for the 5.8 kernel issue I found and they had fixed that a long time ago with a revert so I do not understand why they are doing it again unless they did a rebase and it got left out.
With the current 5.10-rc2 kernel, unfortunately I still have poor hw accelerated video at 4K verses 430 fps with fbturbo. I know it is not apples to apples but it accurately describes the user experience.
$ glxinfo | grep Device
Device: V3D 4.2 (0xffffffff)
$ glxgears
Running synchronized to the vertical refresh. The framerate should be
approximately the same as the monitor refresh rate.
112 frames in 5.0 seconds = 22.221 FPS
107 frames in 5.0 seconds = 21.336 FPS
103 frames in 5.0 seconds = 20.418 FPS
106 frames in 5.1 seconds = 20.806 FPS
109 frames in 5.0 seconds = 21.683 FPS
106 frames in 5.0 seconds = 21.107 FPS
105 frames in 5.0 seconds = 20.886 FPSTo be honest I do not want a 4K monitor with my pi4 and if I did it would only be using fbturbo (llvmpipe) which still under performs.
I just tried the mesa-git but still no good, so back to fbturbo.
I keep hoping to reach good hw performance, so I can try out Plasma on Wayland. It might work well enough to run on my 1080 monitor. But I have higher priorities… like finally trying the f2fs compression, where this began. 
Addition:
I think the 2K monitors are the sweet spot but they are not cheap. But a 4K 43" TV/monitor from Amazon for $230 is a fairly cheap option for a nice display for a RPi4, if you do desktop work… really nice for big spreadsheets or having multiple side-by-side windows open.
Well, it would seem I have f2fs compression functional, I can’t say it appears to work. It is totally transparent and I have yet to find a way to peek inside.
f2fs without compression:
/dev/mapper/vg0-home 29358080 1772500 27585580 7% /home
f2fs with compression:
/dev/mapper/vg0-new_home 29358080 1772376 27585704 7% /mnt/home
Transparent compression… how can one know if it actually works? But it appears to be mounted with compression active.
$ cat /etc/mtab
/dev/mapper/vg0-new_home /mnt/home f2fs rw,lazytime,relatime,background_gc=on,discard,no_heap,user_xattr,inline_xattr,acl,inline_data,inline_dentry,flush_merge,extent_cache,mode=adaptive,active_logs=6,alloc_mode=default,fsync_mode=posix,compress_algorithm=zstd,compress_log_size=2 0 0
So let’s count this as a success until proven otherwise and hope it actually results in fewer bits written to the SSD.
In the gentoo forums they used a command compsize. Do you have that command?
/usr/share # compsize .
Processed 87689 files, 39573 regular extents (40152 refs), 60656 inline.
Type Perc Disk Usage Uncompressed Referenced
TOTAL 62% 1.8G 3.0G 3.0G
none 100% 1.1G 1.1G 1.1G
zstd 39% 760M 1.8G 1.9Gno, but I’ll look around, thanks.
edit: I think that is a command for btrfs.
It is in the repo but it is for btrf.