At its surface, Drupal seems to be a lot of CSS and Javascript being pushed around by lots and lots of PHP code -- these days with healthy chunks of Composer, Twig, and some other things. Inside, though, at its core, is a SQL database. (Usually -- but if your Drupal site isn't running SQL, you're probably not actually interested in simplifying Drupal.)
Taking a peek at the database tables inside of a Drupal site and you'll often see a simpler structure than you see on the outside. Nodes, fields, taxonomy relationships -- it's amazing what you can learn with a few simple select statements. (Want help writing them? Ask ChatGPT, its happy to help.)
Have fun spelunking!