Earlier this day, I read that Strapi is dropping its support for MongoDB. I was a bit bummed at first, but their reasoning was good and I moved from MongoDB Atlas to CloudSQL.

From that point on my day got so much better: Now my strapi backend is so much faster than before! I cannot believe, that I just got to migrate to SQL. Should have done this a long time before.

All operations are literally 2-3 times as fast as before. Thank you @strapiDevelopers for forcing me to migrate :D