Thank you for posting your query on Microsoft Q&A, from above description I could understand that you are looking for advisory on how you would be able to scan and apply sensitivity labels post Azure Information Protection add-in for Office retirement.
Please do correct me if this is not the case by responding in the comments section:
As per Built-in labeling vs. the AIP client, when you keep the AIP client installed but disabled in Office apps, the other capabilities of the AIP client remain supported: "A scanner to discover sensitive information that's stored in on-premises data stores, and then optionally, label that content."
For more information about these capabilities that extend labeling beyond Office apps, see the Azure Information Protection unified labeling client administrator guide from the AIP documentation.
Please "Accept the answer (Yes)" and "share your feedback ". This will help us and others in the community as well.
Thanks,
Akshay Kaushik