You can use the entire life cycle but not one is forcing you to. You can update from one LTS to another every 2 years, or 4 years, or 5 years... you decide.

If possible, it's nicer to pick established, mature software for as much of your stack as you can, so that there's less of a difference in APIs over longer time frames. But it's not always possible.

It is definitely less terrible than trying to unfuck tangles of terraform / terragrunt / yaml / bits of cloud infra.

IMO, the lure of an LTS is that you don't need to keep testing if your computer is still working every week when a set of updates come. Not that things that your software depends on the details remain frozen. If your software depends on the details of something, you should add it as a dependency.