I’m using the official Syncthing Android App and updated my Pixel 3a to Android 11 two days ago.
Syncthing is still working without problems. I can sync (with write access) to
/storage/emulated/0/Android/data/com.nutomic.syncthingandroid/*/storage/emulated/0/Music//storage/emulated/0/Download/
But for other Apps to be able to use the synced data, I had to change /storage/emulated/0/Android/data/com.nutomic.syncthingandroid/* to /storage/emulated/0/Android/media/com.nutomic.syncthingandroid/* as e.g. TotalCommander or Keepass2Android cannot access /storage/emulated/0/Android/data/ anymore.
Syncthing is able to set mtime /storage/emulated/0/Android/media/com.nutomic.syncthingandroid/* as well.
EDIT:
Another Sync-Tool I use is also still able to sync to its directory in /storage/emulated/0/Android/data/{appname}/ but its folder picker cannot list the contents of /storage/emulated/0/Android/data/. Very strange.