Hi Joe! A plugin does not amounts to a full application, however a plugin can be the core of the Bubble application’s experience.
And yes, anything you can build in a normal web page you can build and use in a Bubble app page.
And almost the same goes for server side stuff, but this needs a more detailed conversation.
If you want something robust and do not mind paying, there is my all including course on starting with plugins: New plugin making course with all-included and no-knowledge-spared [15 July 2021] 