IIRC Strapi is a great option for green field projects. C/p from their docs:

"Strapi applications are not meant to be connected to a pre-existing database, not created by a Strapi application, nor connected to a Strapi v3 database. The Strapi team will not support such attempts. Attempting to connect to an unsupported database may, and most likely will, result in lost data."

Unfortunately, most of the time I do not have such luxury. What are the CMS options for pre-existing databases?

I’m curious as to why you need to use a pre-existing database?

Can you run some migration scripts to port the old database content into a new CMS?