renovate/lib/modules/versioning/same-major/readme.md

The 'Same Major' versioning is designed to handle the case where a version needs to treated as a "greate than or equal to" constraint. Specifically, the case where the version say, X.Y.Z signifies a range of compatibility from greater than or equal to X.Y.Z to less than X+1.

This process uses Semver-Coerced versioning beneath the surface, single versions (e.g., X.Y.Z) are converted to a range like X+1 and then passed to the corresponding semver-coerced method.

This method is handy when managing dependencies like dotnet-sdk's rollForward settings. Let's say a project uses dotnet-sdk version 3.1.0. It needs to be compatible with any version in the 3.x.x range but not with versions in the next major version, like 4.x.x.

For example:

{
  "sdk": {
    "version": "6.0.300",
    "rollForward": "major"
  }
}

The roll-forward policy to use when selecting an SDK version, either as a fallback when a specific SDK version is missing or as a directive to use a higher version. In this case with major it means that select the latest version with the same major. ie. >= 6.0.300 < 7.0.0

For such cases, the users would not want Renovate to create an update PR for any version within the range >= 6.0.300 < 7.0.0 as it would not change the behaviour on their end, since it is handled by the manager already.

Note: You should create a discussion before using this versioning as this is an experimental support and might have some edge cases unhandled.