Is there a good style guide for PowerShell comment-based help?

Start with the documentation and comments section of the PowerShell Practice and Style guide. It gives you a community style reference to work from, though you don't have to adopt every recommendation unchanged.

For a comparison, look at the PowerShell documentation source for cmdlet help, such as Get-Process. That can help you see how established documentation separates a short summary, fuller explanation, parameter details, and examples.

For a practical template, keep the synopsis very short. A target under 80 characters is one possible team convention, not a requirement. Use the description for what someone needs to understand before running the command, and give parameters and examples enough context to be useful.

Some teams also write help text with Markdown in mind so it can be turned into local documentation. Check how the formatting reads in the console before making that a standard, though.

Use a function help template as a starting scaffold, then agree on which sections your team actually requires. A template helps with consistency, but it won't decide whether the explanation or examples are any good.

If consistency is the goal, consider Pester checks for the formatting rules you decide on. Automated checks can catch missing or inconsistent structure, while someone reviewing the script checks whether the help actually makes sense.

Also consider whether comment-based help is the long-term format you want for everything. External help and updateable help are worth looking into as future goals, especially if the documentation needs to be maintained separately from the code.