Our two 7 month old kittens were going in their two trays, from when we rehomed them, happily.
They’ve been going out into the garden now, for about a month and the last week have barely used the trays, except for the odd nigh time wee (we keep them in at night).
I’d actually love them to go back to using their trays! Opposite issue to you OP.
I’d like to be able to keep an eye on bowel movements, as well as not pissing off neighbours I really get on with and I’m dreading somebody complaining that they’ve started crapping in their prize dahlias...
One of the girls has crapped in our flower bed once and I said no firmly, showed her the tray, then put little sticks and garlic scat-a-cat powder down, to deter her.
I honey sky don’t mind if they have a little wee now and again, and we’ve kept two areas, close to the house, as bare earth with mulch over it, hoping that would be their spot (if they insist on going outside) but they go anywhere, at random and have progressed from only peeing outside, to also crapping.
They have nice big trays, good depth of litter, lovely litter they always happily used when they were indoor kittens. Nothing else has changed.
I know they are their own masters, but if anyone’s got tips on how to encourage them back to their trays, please pass them on!