In model mode at the SQL endpoint of my LakeHouse, I try to add a tab beside the 'All tables' and create relationships. The browser will refresh, and my new tab is gone. The relationships stay, but the 'All tables' tab is re-organized to a default view.
This question appears to be better suited for theSynapse communitywhich does cover Warehouse related topics. This community focuses primarily on the components found inside of the Data Factory which are, today, Data pipelines and Dataflows.
I'd encourage you to post this question on the Synapse community.