So…CCC seems to be a very basic inventory management solution. What this generally describes is a system compromised of a database with a front-ends that makes sense of whatever the particular project is (car repair), and provides an easy to interact with the database.

What you’re using now is simply for workflow management of projects in a simplified way, which is probably not what you want.

So you need a database, and you also want an easy way to interface with it, so you can check out the plethora of inventory management solutions in the FOSS space, but if you want something pretty simple that you can more easily customize for your needs and workflow, have a look at the FOSS alternatives to Airtable like nocobase. You set up a simple data structure, then can slap together quick forms to work inside of with whatever fields and data you choose. Dead simple, but very extensible.