Creating multiple apps (same code but different DBs)

I have created a solution that allows many users to use the same solution - the data is effectively locked to a type of company.

However a client has asked if it would be possible to run a solution that only contains their own data - dedicated DB. Obviously I don’t want to have lots of different solutions as every change would need to be made in each solution.

Therefore I wondered if there is a solution for the design/workflows to be potentially shared (or even linked) but the DB’s to be separate.

One answer would be separate apps with lots of control between them (probably manually) and then use sub domain names from the main domain name to point to different locations…

Hopefully that makes sense but would be keen to get peoples thoughts/experiemce - not sure sub apps would do it?