Unlinking or in any way creating 2D drawings is an absolute last resort thing that should be avoided if at all possible. Try to keep your model and all drawings live at all times.
In AC 20, the new Graphic Override (GO) feature can be used to change the appearance, including line weight, of elements in your elevations. Like most other settings, this is saved per-view, so you can customize each view of those elevations.
http://helpcenter.graphisoft.com/guides/archicad-20/archicad-20-reference-guide/views_of_the_virtual...
In AC 19 (your signature) - and AC 20 - Pen Sets are a way of assigning different weights (and colors) to the same pens in different views. A pen set is associated with each view.
http://helpcenter.graphisoft.com/guides/archicad-20/archicad-20-reference-guide/configuration/attrib...
Check out each of these features in the documentation / videos / etc to see which works best for you.
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AC 28 USA and earlier • macOS Sonoma 14.7.1, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB