While creating a pre/post deployment step, you have the option to select specific environments. That list does not contain all the connected environments within our pipeline. It seems to only show environments that are along a direct downstream path of the step's source.
With all of Gearset's automation and back-propagation functionality, it is possible for that PR/step to arrive at an environment that isn't along a direct downstream path of the step's source. Because of that, I would expect to be able to account for all environments in a pipeline while creating a deployment step. We often have steps that are only needed in specific environments e.g. "only in Prod", "only in pre-prod static orgs", "only in developer sandboxes", "only in 2 specific orgs", etc. This issue means we currently have no way to manage this within Gearset and need to resort to tracking it in an external system like Jira.