I'm sure this has happened in prev versions, but currently in version 25.3;
If you are loading a REC2100 HLG clip into a time line, the thumbnail will have the proper colors, and not be blown out.

If you change to an SDR sequence, the preview window/program monitor all do whats expected, but the thumbnails have blown out color. (a little harder to see with this example, but it is there, other clips produce more blowout depending on what it recorded).

Hopefully someone at Adobe can address the color management on the timeline also please.