Oddly enough, this isn't my first post on linen napkins: https://www.thesingletable.com/post/oopsies-what-to-do-when-your-guest-dirties-that-white-linen-on-the-table
In many fine-dining restaurants, when a guest goes to the toilet, often a member of staff will come by the table and re-fold the napkin.
BAN THIS IMMEDIATELY.
Not only is this an added touch point for the guest (because I might as well suck on your thumb), but the server will be picking up "mouth debris" all night and then cross-contaminating the entire restaurant.
Yes, I know linen laundry is insanely expensive. But, if you're going to offer a linen napkin, you need to replace it if a guest goes to the toilet or don't touch it. In fact, if my napkin wasn't touched after a return from the toilet, I consciously fold it over so that nothing that touched the table will touch my mouth.
Recently, I've seen the napkin replaced with tongs which is how it should be done so it's the most sanitary solution possible.
Yes, your napkin has been touched by someone at some point, but we need to be mindful of how to make the restaurant as sanitary as possible.
If I've gone to the toilet and I see the napkin has been touched, but not replaced, I simply ask for a fresh one.