Welcome to the Strapi Community @Niklas_Rapp
Because Strapi is built on NodeJS, you can always just extend things yourself. It really depends what you are doing.
But you can use the firebase SDK to extend functionality etc.
Remember that Strapi V4 is MYSQL and you are trying to store NOSQL data so it’s different database schemas.
So no sadly there is no “connectors” etc except for the firebase SDK