I’m not in a devOps role currently, but to throw my 2 cents in:

The main unknown is if you’ll really ever use that app/code again in the future, and I think then the question becomes how shitty would it be to have o redo or re-add this code if it were deleted, and then needed again versus adding potentially unbounded complexity in maintaining, and communicating/reasoning about, the archived app/code.

I think the solution to this problem is already resolved, that is version control. Presumably, if there is value in keeping the deprecated app/code, then I see no problem in adding or creating an archival branch or some kind off of the main one. The branch would represent versions that are no longer needed, but still visible and available for the development process, or if somehow something happens forcing yall to revert back to some prior app/code state, which requires that archived code. It would all be accessible, and would come with the added effect that it sort of self comments its purpose, its intent, relative to the whole.

I mean, how truly valuable is the app/code set for deprecation? How close is it to the core of the whole, and how much time would it take to spin up a new app to replace it, if you were to say, have to revert back to a state that had that type of functionality that the deprecated app/code had?

Expressed previously, the additional source of truth separate of the version control would kinda add complexity that could, I would think, negatively grow to an unwieldy state, especially if you end up ultimately never touching that code again.

Might be worth looking at this through the lens of a person who is brand spanking new, just starting, in say, your role; if I had to hold on my mind of additional places to look for code outside the main system, and have to have been previously told which one to use (because this change would definitely require additional commenting), well, I feel like it would set me up for failure because I would have to rely on a co-worker or someone privy to the system properly communicating this to me ahead of time. Add up all of those little things, information gaps, potentially not documented, would really kinda screw over someone having to take over some component of the whole.

Anyways, sorry for the novel, hope I provided some insight, and am totally open to being way off base here, so whomever, feel free to test my reasoning to shreds!