MongoDB Atlas is a nice option. Not free but quite cheap for smaller scale. Also check out Supabase and Render - not NoSQL but generous free tiers.

Supabase developer here: keep in mind that, while PostgreSQL is unapologetically SQL-based, it's support for JSON and JSONB fields give it a lot of the powers of NoSQL. These days the lines are becoming more blurred.

Here's an article I wrote with a basic introduction to the NoSQL features of PostgreSQL: https://supabase.com/blog/sql-or-nosql-both-with-postgresql

I never thought about it this way, but it is nice and interesting browsing my upvote history. So probably in a subconscious way - yes.

It depends on your stack and app type, but I had great experience with Ghost Inspector https://ghostinspector.com/

This style of explanations is awesome. Check out Bartosz Ciechanowski's stuff for a few masterpieces - https://ciechanow.ski/