How to properly divide an application into front-end and back-end?

Question

JavaScript

There is a very large java back-end + front-end application now everything is in one git repository, it looks something like this:

project:
-moduleX:
...
----java
----webapp (тут весь front-end)
-moduleY:
...
----java
----webapp (тут весь front-end)
-moduleZ:
...
----java
----webapp (тут весь front-end)

Due to the fact that the authors of all this miracle wrote it so that it will not be possible to divide it into microservices in a reasonable time. Therefore, I want to split this into at least 2 parts front-end and back-end and the only idea I have is to make a git submodule (pull into separate repositories) from the webapp content in each module.
I need this so that I can independently deploy the server and client, i.e. upon release, I would separately collect all js into bundles and in jsp I would only indicate a link to the server that would give js.
What other options are there to separate the front-end and back-end with this "architecture"?

Answer 1

I would suggest moving the back-end into separate REST API/GraphQL and one of the front-end projects on SPA (React, Angular, Vue) piece by piece. With translation and experience, you will grow and the architecture will settle down.