This is the current behavior of that button, for more fine grained control, you have a few options.

1. Put the services into a group, open that group, and then the sync button will be scoped to only changes possible within that group.

2. Use the service context menu's 'sync to' and 'sync from' on individual services.

this feels like an issue, because shared envs live outside of the canvas and ideally there should be a place where one envs is not force into others. Does this happen even if we seal the variable?

maybe only add missing key fields, or only allow merging when specifically in this page, because there should be at least one place this is not the default, since its common for variables to be different and stay different in some envs

Sealed variables are excluded from the sync diff, so they would not be overwritten during a sync.

For the broader request around sync not overwriting environment-specific shared variable values, that sounds like a feature request! Can you write up a detailed explanation of your use case and the feature? This way other users can upvote your issue and help us prioritize it.

You can write your feature request and view the roadmap here --->
https://station.railway.com/roadmap

https://station.railway.com/feedback/granular-control-over-shared-environment-2a5f8883

done