I did an edit using JPGs and converted them to DNG files to use in LRTimelapse. I cannot find how to render the files in Lightroom Classic or do I have to use the render tool in LRTimelapse only?

Normally the workflow would be to convert the JPG files to DNG in Lightroom.
Then with the DNG sequence you can do one of the regular LRTimelapse workflows, either the Workflow with Lightroom (explained in the Basic Tutorial) or the internal Workflow (explained in the Tutorial about the internal Worfkflow).
Check out the tutorials on https://lrtimelapse.com/tutorial/basic

If you want to export via Lightroom, you open the Export Dialog and choose one of the LRTimelapse templates on the left.