Yes, you can connect any database you want and work easily with it as you can do in Node.js.
You can add any NPM package support and use it in custom APIs.
API Maker gives you tons of features, but it also provides you low level features, so you can extend its capabilities.
Examples:
Using native SQL query feature, you can run any complex SQL query over database. You can also execute procedures created inside DBMS.
You can override default Docker file, and you can use any OS or any OS packages or any program that is built in any other programming languages.
Generated & created APIs, you can consume from any other backend technology also, so you can keep your legacy code running and slowly migrate on API Maker.
API Maker can not do video and audio streaming.
Things which you should not develop in Node.js, should also not develop in API Maker.
Work around: You can keep that module separate with your API Maker backend, and they can easily communicate with each other.