it is Fixed.
So, after a really long search and by pure chance, I found the bug causing the Social Menu and tiles not to work for me.
For various reasons, and long before installing BF6, I had changed my environment variables TMP and TEMP. Instead of pointing to "%USERPROFILE%\AppData\Local\Temp", they pointed to my second drive (also a fast M.2 SSD) at "d:\Temp\_twobnt\sys_temp\".
I naturally checked the access rights and adjusted them to match the original path when I set this up over two years ago. The entire system and almost all programs that use these variables worked perfectly, storing their temporary files in that custom directory.
I didn't delete the original path, knowing that some programs derive the path to "%USERPROFILE%\AppData\Local\Temp" differently than via environment variables. As I said, these settings always worked very well. BUT, BF6 cannot handle this shift of environment variables within the menu tiles and the Social Menu. In BF2042, it was only the menu tiles that weren't displayed (this bug appeared in BF2042 via an update about 2–3 weeks after the release of BF6).
By resetting to the default values:
setx TEMP "%USERPROFILE%\AppData\Local\Temp"
setx TMP "%USERPROFILE%\AppData\Local\Temp"
and rebooting, all errors are gone and BF works excellently.
If I switch it back to the custom path, the errors return immediately after a reboot—it is 100% reproducible.
Yes, I had seen the hints regarding environment variables. However, I only checked if both existed and pointed to a directory with the correct permissions—which they did. Who on earth would expect it not to work?
I suspect the following error on EA's side: One part of the EA/BF software downloads the necessary content via "%TMP%\Battlefield™ 6", while another part of the program tries to access it via "%LOCALAPPDATA%\temp\Battlefield™ 6" (or vice versa).
This can only work if you use the default values for both environment variables. Otherwise, they point to different directories.
I will communicate this solution directly to EA so they can investigate.
I hope this helps others!