Maybe you could do something like this:
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Create a new parent deck to group all your old Anki decks (you can move them by renaming/dragging them)
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Set parent deck’s new and review limit to 0
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Collapse the parent deck to hide your old decks
In addition, you can suspend all the cards (e.g. by going to the browser and searching deck:Archive → Ctrl+A → Ctrl+J), to make sure they will not get included when creating filtered decks or custom study sessions.
Alternatively, if you do not want to see the old decks and their cards at all, not even in the Browser, maybe you could export a backup copy of your collection (including media and scheduling info) and then just delete the unwanted decks.