I'm still new to Jira, but I've already researched a lot into the ecosystem as much as I could because I'm aware it's possible to develop for Cloud and Server at the same time to an extent (Client-Side UI, REST API).
I am not sure which Connector I should use in order to have a API that can be used for both. Such as using Conector for Nodejs because I want to use Atlaskit and React, or for Springboot so it Java can access it for Server as well.
Apps for Server and Cloud are very very different beasts, you won't get a lot of sharing done (unless your tactic is to run a remote service like Cloud Apps and work exclusively remotely). You'll also find that the Cloud and Server REST APIs are not identical because the products are diverging.
Welcome to Atlassian Community.
I believe there is no Atlassian Connector that would be supported in both Jira Cloud and Server with the same API, however, I believe that our developers and third-party can give you more information about it in the portal below:
The mentioned portal was specifically created for development questions, where you will find articles and suggestions from other third-party partners and Atlassian developers. Feel free to open a new topic about your question there! :)
Have a nice day and let us know if you have any other questions.
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