@mitchell-demol we do not currently support setting an env var in a step and have it be available in a subsequent step on any OS. Please refer to this link:
https://discuss.circleci.com/t/passing-variables-to-other-steps/27700
The recommendation would be to write to a file and read the values back in, or read/write to the registry.
I can make a recommendation that this be supported in the future.
Thank you,
Mike