Letting the action fail might be a bit harsh for backwards compatibility reasons, how about a warning message?

# The repository will be downloaded using the GitHub REST API
# To create a local Git repository instead, add Git 2.18 or higher to the PATH
! WARNING: Some options are not available when using the Github REST API

1. No one is reading logs until errors
2. It will just crash later on when you want to use Git or may have strange/unpredictable behavior if trying and just ignoring in case of failure.

No one is reading logs until errors

I think it's quite common to check logs when creating or adjusting a workflow. However, once a workflow is up and running, I agree.

It will just crash later on when you want to use Git or may have strange/unpredictable behavior if trying and just ignoring in case of failure.

Let's assume this really would lead to crashes in most cases, how many users are relying on the current behavior because they build workarounds or adjusted their workflows accodingly? My feeling is that such a breaking change is too risky and may even lead to a net negative impact in the short/mid term.

Some ideas for further discussion:

• Release in upcoming major version
• Introduce boolean field exit_on_mismatch to on/off the proposed functionality
• Add warning message

adding on exit flag defaulting to off sounds good to me ! This is the best trade-off.