How would I start versioning a Software with Multiple Components

I am working on a multi contributor project, having ~2500 Commits. It has multiple components, i.e. Frontend, Backend and Data Processor/DB Ingestion.

Now that we are expecting more contributors, a Versioning System should be implemented, and should be displayed on footer of Frontend, as vA.B.C, where A = Big Change, B = New Features and C = Patch Fix. But, the issue is that we are having a very complex multi component software and has many commits.

How should I approach this?