Would love to be able to select multiple branches for the PR previews. Right now we need either two projects that point at staging and production branches, or we need to have one project but switch which branch that project is pointing at based on which branch we need PR previews from. For Heroku review apps, I think they do this (or they may just do previews for any PR created in the project).
Unfortunately, there’s no way currently to specify multiple branches without creating two services. You’ll be able to do this with our upcoming work on service grouping, which we’re tracking at https://feedback.render.com/features/p/visual-service-grouping, so I recommend following that feature request so you’ll be notified when it’s ready. I know the engineering team is actively working on it, but it’s a big feature, so we’re not yet ready to promise any dates.
Sorry for the late reply! Yes, preview environments won’t build an environment for every PR in the repo. Specifically, it will only build an environment for PRs that is targeting the branch that you specified when you first created the Blueprint.
For example, in the screenshot below, only PRs targeting master would have preview environments built.