Im making a UI but it’s hard to edit the items under the background frame. How do you lock it like BaseParts in the workspace to where you cant select it in the viewport?

Try this, if this doesn’t solve your problem I will try again.
this wouldnt solve the issue from 4 years ago
this isn’t a feature or property itself but holding ALT may do something? other than that there is a way to do this by making a plugin to add in this feature.