You can do that, but there are a couple of things to keep in mind.
Different apps may only be compatible with certain database products and versions. I could be a real pain if you have to spin up a new version of a database and migrate just for one service that updated their dependencies or have to keep an old database version around for legacy software.
If you stop using a service then it’s data is still in the database. This will get bloated after a while. If the database is only for one service then wiping it out when you are done isn’t a big deal. However, if you use a shared database then you likely have to go in and remove schemas, tables, and users manually; praying you don’t mess something up for another service.
When each service has its own database moving it to another instance is as easy as copying all the files. If the database is shared then you need to make sure the database connection is exposed to all the systems that are trying to connect to it. If it’s all local then that’s pretty safe, but if you have services on different cloud providers then you have to be more careful to not expose your database to the world.
Single use databases don’t typically consume a lot of resources unless the service using it is massive. It typically is easier to allow each service to have its own database.