From what I can gather, yes[1]:

A dump/reload of the database or use of the pg_upgrade application is required for major upgrades.

Now, seems one can mostly use pg_upgrade, which only rewrites the system tables[2] so is fairly quick. But if on-disk format has changed it seems you're forced to dump and reload.

At work we've mainly been using SQLAnywhere, which would just disable new functionality for databases using old on-disk format. So upgrading major versions has usually been fairly painless and quick.

[1]: https://www.postgresql.org/support/versioning/

[2]: https://www.postgresql.org/docs/current/pgupgrade.html

Well if it's self-hosted you have to do it yourself. You can either backup your databases from the old version and restore it to the new version once installed, or you can use pg_upgrade to upgrade/copy a old version data directory to the new version.

I don't think this is done automatically when you simply install a new postgres version, but I'm not certain of that.