The general advice is to always upgrade to 3.11.latest before upgrading to 4.0.latest. It is possible to upgrade from an older 3.11 version but you'll probably run into known issues already fixed in the latest version.
Also, we recommend you run upgradesstables BEFORE upgrading to 4.0.latest -- this is to make sure there are no old sstables lying around. If there are no old sstables to upgrade, the upgradesstables is a no-op so it's no big deal. And definitely run it AFTER you've completed the binary upgrade to 4.0. It doesn't need to happen immediately and can be postponed for off-peak periods. Cheers!
