I had the same issue in Microsoft Word and have now found what was causing it on my system.
The text was actually being selected correctly, but the selection highlight was not displayed correctly on the monitor. When selecting multiple lines of text with the mouse, only the first line (or part of it) appeared highlighted. However, the entire selected text could still be copied with Ctrl+C, formatted, deleted, etc. Ctrl+A also selected the entire document correctly, even though the selection was not visually displayed.
Interestingly, when I recorded the problem using Windows Snipping Tool screen recording, the full selection highlight was visible in the recorded video, although I could not see it on the monitor while making the selection. This indicated that the selection itself was working and that the problem was related to rendering/display rather than mouse input or Word's selection functionality.
I also tested Word in Safe Mode, but the problem remained, so disabling Word add-ins did not resolve it. Enabling Windows Mouse ClickLock also made no difference.
The issue was resolved by disabling “10-Bit Pixel Format” in AMD Software: Adrenalin Edition and restarting Windows. After the restart, text selection highlighting in Word immediately worked normally again.
Importantly, disabling AMD's “10-Bit Pixel Format” does not require disabling 10-bit output to the monitor. My AMD Display settings still show Color Depth: 10 bpc and RGB 4:4:4 Pixel Format PC Standard (Full RGB), and Word selection highlighting now works correctly.
I also tested with Windows HDR disabled, and Word continues to work correctly. Therefore, in my case the relevant setting appears to be AMD's 10-Bit Pixel Format, not the monitor's 10 bpc color depth or Windows HDR.
System configuration:
- Windows 11 Pro 25H2, OS Build 26200.8875
- Microsoft Word for Microsoft 365 MSO, Version 2607 (Build 16.0.20228.20124), 64-bit
- AMD Radeon RX 6800 XT
- AMD Software: Adrenalin Edition 26.7.1
- Display connection: DisplayPort
- Color Depth: 10 bpc
- Pixel Format: RGB 4:4:4 Pixel Format PC Standard (Full RGB)
- Windows HDR: Off
- AMD “10-Bit Pixel Format”: Disabled
The issue had been present on this PC for approximately a year, so it does not appear to be specific to AMD Software 26.7.1. I had used multiple AMD driver versions during that period, although I did not test Word after every individual driver update.
Hopefully this helps others experiencing the same problem, especially since disabling the separate AMD 10-Bit Pixel Format option still allows the display output itself to remain at 10 bpc.