10+ Sites Suddenly Dropped in GSC, What Gives?

I have 10 - 20 sites that would rank on Page 4 - 6, not the best, but hey. The sites are approximately 1 month old. Upon launch and importing to GSC, they were ranking pages 4-6. Now, this week all of a sudden, I am either 1) not ranking or 2) ranking in page 9-10. No major changes or updates. The impressions were about 1k daily across domains but now they're basically 0. Someone suggested working on Topical Authority, however, I was ranking on pages 4-6 upon launch within a couple days of importing to GSC and submitting the SiteMaps. Thought? Is it Topical Authority or a stealth update to SERPs? No manual actions.