SQLite is alway serializable and by default has synchronous=Full so fsync on every commit.
The problem is it has terrible defaults for performance (in the context of web servers). Like just bad options legacy options not ones that make it less robust. Ie cache size ridiculously small, temp tables not in memory, WAL off so no concurrent reads/writes etc.
CockroachDB is serializable by default, but I don’t know about their other settings.
FoundationDB provides strict serializability by default.
Pretty sure SQL Server won't acknowledge a write until its in the WAL (you can go the opposite way and turn on delayed durability though.)
One of the most used DB in the world is Redis, and by default they fsync every seconds not every operations.