Here is a suggestion from my recent experience of upgrading to an LTS version (6.7 LTS -> 7.9 LTS).
Would it be possible to have a Release Note specific to the new LTS version which synthesizes all the changes since the previous LTS version?
Such a Release Note would simplify the preparation of this kind of updates by allowing faster identification of breaking changes while avoiding the tedious unstacking of all changlogs of non-LTS versions.
It was, for example, in the release note for version 7.7 that I discovered that the sonar.language key had been abandoned. It is typically this kind of information that you need to know to anticipate an LTS version upgrade.