Hello, I hope this post proves helpful to someone facing the same issues I did, allowing them to enjoy this monitor for a longer duration. I've been a longtime observer of this thread and find it immensely beneficial, filled with great information for fellow 5K UltraFine owners. So, thank you to everyone who contributes here.
I purchased my monitor (model 27MD5KA-B, dated 2017) used in 2021 for $700 on Craigslist during the pandemic. Initially, I used the monitor with a 2019 16" Intel MacBook Pro, and later upgraded to an M2 Mac Mini. This being my first 5K monitor, I must admit I didn't pay close attention initially, so I'm unsure if the issues I have were present when I bought it or developed over time.
The monitor exhibits image retention issues at the top and bottom of the screen; the dock and top menu bar tend to get burned in. Additionally, there's a noticeable "pinkish-red" hue in the four corners (which I believe is backlight bleed). I've observed that these issues are most pronounced on a specific grey color, particularly noticeable in Google search. It's worth noting that I exclusively use dark mode.
I've spent hours searching for solutions and tried various suggestions to improve the mentioned issues (e.g., changing color temperature, lowering brightness), but to no avail. Both ghosting and the hue worsen with prolonged use, and they seem to intensify as the display warms up (I assume). While ghosting temporarily disappears with "burn-in fix" YouTube videos or a "TV static" video, it quickly returns.
Initially, I used an old 1st gen 12.9-inch iPad Pro as a secondary display with Sidecar, which I found enjoyable. However, over time, I noticed the GUI became sluggish on my monitor, later discovering that Sidecar was the cause (though I'm unsure if this issue has been resolved since I stopped using the iPad).
Since I valued having an extra display, I purchased a cheap monitor from Amazon, the LG 27GL83A-B, which works well but has limited compatibility out of the box with macOS. Discovering Better Display, I bought it to enable HiDPI and brightness control. Interestingly, Google appeared darker on the secondary display than on my 5K UltraFine, prompting me to experiment with Better Display's settings for the LG UltraFine. Increasing contrast in the image adjustment setting from the default 0% to 15% turned the "gray" Google website black, eliminating the pink hue and image retention! While I can't say for certain if this is a placebo effect, I feel like my monitor has been revitalized. Everything looks significantly better with this contrast adjustment. I'm unsure if the factory contrast calibration has changed over time, but the difference is remarkable. It's as if I have a new monitor!
Apologies for the lengthy post, but I hope it proves helpful to someone experiencing similar issues, as it has restored that "wow" factor to my UltraFine display.
TLDR: Change contrast setting if you have Pink HUE issues and image retention that is visible on grey colored websites apps.