After CLM 6.0 upgrade baseline icon is missing in artifacts history page
3 answers
RDNG 6.0 no longer has module baseline feature(as configuration management feature is introduced, it has project baseline feature), therefore, you won't see any artifact baseline icon in the history.
The following Work Item may be applicable: UI: https://jazz.net/jazz03/resource/itemName/com.ibm.team.workitem.WorkItem/94585
The following comment may address your concern:
"After an upgrade to v6.0 all baselines [both Module and Artifact] are set as archived. If you go to the cog menu and select 'manage baselines' and click the 'show the archived configurations' button do you see content? When you restore them, they get reindexed, and will show up in the configuration picker when indexing completes. My recollection is that this was done for performance reasons and it makes upgrade faster, and will also mean fewer indexed resources. "
After restoring the archived configurations the older baselines that were present in the earlier version of RDNG should now be visible for selection