Update macOS version support documentation

[scpeters]

Desired behavior

Our macOS support currently relies on homebrew, which provides no more than 3 years of support for a given version of macOS (see brew support tiers documentation). The Gazebo Getting Started page currently lists macOS Monterey and Ventura as supported for Harmonic, but Monterey is no longer supported and Ventura support will end in about 1 month.

We should clarify what our macOS support actually entails.

Alternatives considered

Implementation suggestion

Additional context

[scpeters]

I've distilled the relevant information about Homebrew and macOS support windows into the following, along with an articulation of how we currently support Gazebo on macOS with homebrew:

Background:

Gazebo is currently supported on macOS using the Homebrew package manager with formulae hosted in the osrf/simulation tap. Homebrew is a “rolling-release package manager” that tries to “ship the newest things as quickly as possible,” leading to frequent changes in the default versions packages like protobuf and python that Gazebo builds against.

Per Homebrew’s Support Tiers documentation, a Tier 1 supported configuration will provide the best experience using Homebrew, including CI coverage and bottles (binaries). Homebrew provides Tier 1 support on macOS for 3 versions of macOS at any given time, the latest stable or prerelease version and the two preceding versions. New versions of macOS are typically released in September of each year. Until September 2026, Homebrew’s Tier 1 support includes both Apple Silicon (arm64) and Intel x86_64 (amd64) architectures. After support for macOS 27 is added in 2026, Tier 1 support for Intel architectures will be dropped.

Gazebo releases a new collection each year in September, with recent versions alternating between two years of support and five years of Long-Term Support (LTS). While there are macOS versions with Tier 1 support for a two-year span, no single version will have Tier 1 support for the five-year span of an LTS release.

Current support level for Gazebo on macOS

I’ve attempted to articulate the current state of support for Gazebo on macOS:

• All stable releases of Gazebo are supported on macOS with Homebrew for at least two Tier 1 versions of macOS at any time with CI and binary bottle builds. For example:
  • Sept 2025 - Aug 2026: arm64 support on macOS Sequoia 15 and Sonoma 14, and Intel x86_64 support on Sonoma 14
  • Sept 2026 - Aug 2027: arm64 support on macOS Tahoe 26 and Sequoia 15
  • Sept 2027 - Aug 2028: arm64 support on macOS 27, macOS Tahoe 26
    etc
• Due to Homebrew’s rolling-release properties, the specific version of dependencies used by Gazebo may change at any time. These dependency upgrades often break Gazebo’s ABI, necessitating package rebuilds. Changes that break API will be handled on a case-by-case basis.

[scpeters]

I made a suggestion in https://github.com/gazebosim/docs/pull/645/files#r2462138504 with a minimal update to our documentation to reflect which macOS versions we support

[Crola1702]

I think this is pretty much clear. Thank you Steve!