This is the source code for the UMAP to UEFN converter that SenseiUsagi has created, and I have modified. With it you can convert .json versions of .umap files into a format that can be copy-pasted into UEFN. To get .json versions of .umap files use FModel.
When converting .umaps like this the probability of them validating in UEFN is extremly low because it uses assets from the game itself, instead of the ones available in UEFN.
This website was writting in mostly TypeScript, React, as well as React-Router for the routing.
If you have any feedback, please open up a new issue.