I agree that paid/cloud does not necessarily equal lock-in. I mean, an Ubuntu VPS is identical-enough (usually) across clouds. Managed databases? Maybe? what about available Postgres extensions etc.
There are lots of cases where deployment needs some kind of customisation. This usually happens either around persistent state or around building in CI. E.g. in one project some years ago, we wanted to test in CI against a subset of the production database. So there has to be a script to appropriately subset this, not easy if you have complicated foreign key relationships, and you have to make sure confidential data did not make it across. We were not the only people to do this I've seen this elsewhere.
Other example, my previous project: the main framework is Django with a React front end. The admin interface is django html templates. But one of those templates has an embedded additional react component because on that admin page we needed more interactivity. So that has to be built. And all of this has to be tested in CI.
What does non-standard deployment look like? Here is one example. For my current project I use wildcard domains so users can create their own tenants on their own subdomain. This would not work on e.g. heroku or similars, at least i don't know how.
All of this could probably be done in Kubernetes but also much simpler with bash scripts and systemd units.
