YouTube Chapters, built by Film Tools, is a Premiere Pro extension that generates a formatted list of chapters. Once created, the list can be copied and pasted directly into a YouTube video description, where it creates chapters for the uploaded video.
The extension works from markers placed in your Premiere Pro project. A recent update refined how it handles the start of a sequence: it no longer adds an automatic entry at 0:00 when a marker already sits at that point, avoiding a duplicate first chapter.
Listed on Adobe Exchange, YouTube Chapters is compatible with Premiere Pro 9.0 and later. This card lists it as free, so check the developer's page for current licensing. The current release is version 0.2.1, last updated in August 2023.