Can you render videos on a server
Yes, it is possible. Such a concept is often called &quot;render farm&quot;.
On the server side you could use tools like ffmpeg that can concatenate videos. To call it you could build a dedicated render service which works like a job management agent (think of sth. like Jenkins). The goal is to decouple the render jobs from whatever service/API your app talks to.
Maybe you can even use Jenkins because it has a REST API that enables you to trigger builds. Instead of a classic build job, your job will combine videos. This approach might save you some time.
However that is just a recommendation, other architectures are possible.
On the client side, there is one possible problem to be aware: all the raw video material needs to be uploaded to the server and bandwidth or uplink speed could be a limiting factor at some point.
On the server side you have to watch out for possible DoS attack scenarios and upload of malicious content.