Turso's SQLite fork libSQL[1] has an extension/improvement that adds the ability to alter columns and drop constraints (albeit not via a DROP CONSTRAINT clause). I'm not affiliated, but have been using libSQL recently and am finding it to be a very pleasant experience.

Although conceptually I agree that SQLite's limited type system is frustrating, if your usecase allows, an ORM might help with not having to think about it or touch it directly.

[1] https://github.com/tursodatabase/libsql/tree/main