Welcome. The answer depends on which version of AC you are using. I'll assume it is 17. If you click the text link "Profile" near the top right of the page... and to the left of "Log Out" you can add your version and machine specs (OS/etc) to your signature so that people will be able to better answer your questions.
Layer Intersection groups are the most common way to keep interior walls from joining / cleaning-up with exterior walls:
http://helpcenter.graphisoft.com/archicad-18-int-reference-guide/configuration/attributes/layers/use...
A new alternative in AC 17 and higher is Priority-Based Connections in which the building materials for the interior skins would be set in such as way to clean up as desired with exterior composite walls. E.g., the gypsum board would clean/wrap, but the interior stud cavity would not penetrate the exterior insulation:
http://helpcenter.graphisoft.com/videos/archicad/3d-modeling/archicad-17-new-features-priority-based...
AC 28 USA and earlier • macOS Sequoia 15.3, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
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