This can be done within sections using CSS:
* mw-archivedtalk
Or at a page level using a magic word:
* __ARCHIVEDTALK__
"archivedtalk" still detects the comments, but disables features
as appropriate for an archived conversion, i.e. the reply tool.
Bug: T295553
Bug: T249293
Change-Id: Ic47693e9a2f53f92563ccdd50203fb55c12d0493