Or force the big RDBMS to use the same syntax like SQL was intended to be, so I don't have to reach for an ORM or maintain different flavors of the same query.

If someone knows a tool that reliably converts PostgreSQL queries to something like SQLite, please share!

Not sure how such a tool could possibly exist, given all the functionality of Postgres that SQLite simply lacks.

You could ask ChatGPT to do this sort of conversion

Still not going to have wave around things like not having transactions or proper trigger functions.

SQLite does have transactions. But I do agree with your general point that Sqlite is worlds apart from Postgre

haven't really tried for that transform but have a look at https://www.jooq.org/translate/

sqlglot might be what you are looking for.

https://github.com/tobymao/sqlglot