In other programming languages there are versions that have been marked as long term versions in terms of support for features and functions. (e.g. Java 17 LTS), does Apple also have something like this (e.g. Swift) and if not, why not? As a developer, how can you use an app in the long term without functions or features that are suddenly deprecrated?
does Apple also have something like this
No.
As a developer, how can you use an app in the long term without functions or features that are suddenly deprecrated?
Avoid using Apple features; use third-party alternatives, or write your own.
Note that “deprecated” is not the same as “removed” — things marked deprecated generally continue to work fine in later releases. There are a few outliers that have changed more abruptly (e.g. fetching the device name or telephony information) but those tend to be privacy improvements and probably wouldn’t be grandfathered in an LTS arrangement anyway.
Also note that users don’t expect apps to have “long term versions” that never get updated; active apps get new features or just bug fixes at least a few times per year and often every week or so. I personally won’t download any app that doesn’t appear to be in active ongoing development, judging by the release history.