Disable catalog categories without impacting in-progress PRs

Summary:

We are looking for options to disable certain purchasing categories from LOV for selection while creating PR.

Since there are In-progress PRs in these categories, we want the categories to be active but should be hidden from the user for selection while creating new PRs. (Note: All these are non-catalog PRs and there are no items associated with these categories)

This will help in gradually clearing the in-process PRs and then End date the categories.

Please suggest what is the best available option to achieve this.