**System Information**
Operating system: Linux-5.11.0-37-generic-x86_64-with-glibc2.31 64 Bits
Graphics card: NVIDIA GeForce RTX 2070 Super/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 470.57.02
**Blender Version**
Broken: version: 3.0.0 Alpha, branch: master, commit date: 2021-09-29 10:03, hash: `rB4cf4bb2664eb`
Worked: 2.93.4 and 3.0.0 master from a few days ago
**Short description of error**
Data Previews like thumbnails for objects or collections are no longer saved inside the blend files.
**Exact steps for others to reproduce the error**
No blend file to upload here sadly, but an easy description of the problem instead:
Generating Data Previews has always been a bit "flaky" before, e.g. this option in the file menu never worked for me. It always felt like it did "nothing" at all.
{F10669443}
I always used the "Batch Generate Previews" option instead which depending on the scene complexity took some seconds or minutes and re-saved the blend file with the thumbnails inside. The resulting blend file was slightly larger of course because of the added data.
Now with the latest 3.0 master the "Refresh Data Block Previews" finally "does something" and you can see the CPU get some work after clicking it. After manually saving the blend file afterwards it still has the same size. Apparently nothing was added.
When using "Append" or "Link" to open the blend file's internal folder structure there are no thumbnails under "Objects" or "Collections".
When trying to browse this file in 2.93.4 the thumbnails are missing as well.
When using 2.93.4 with "Batch Generate Previews" everything works as expected and the thumbnails are written and even 3.0 master can show them.
Just a shot in the dark but I guess this is somehow related to the new Asset Library stuff that's currently being added.