Depending on the use case (SaaS offerings with per customer shards) you can actually scale sqlite quite high. Expensify scaled to 4 mio qps (queries per second) [1], so if one of your customers is exceeding that, you better be looking at another DBMS but below that - well sqlite is an option.

[1] https://blog.expensify.com/2018/01/08/scaling-sqlite-to-4m-q...