How can I suspend Audible on an Apple account?

I have at one time suspended mine, but I was subscribed directly, not through Apple.

The following seems to rule out the possibility if the membership was started in the iOS app. See this from Audible support https://help.audible.com/s/article/can-my-membership-be-placed-on-hold?language=en_US

Yes. Audible Plus members and Audible Premium Plus members with monthly plans can place their account on hold one time every 12 months. That hold can be anywhere between one to three months. Customers who are on credit-earning plans will not receive credits during their hold. For memberships started prior to 2006, older plans that don’t earn credits, memberships started in the Audible iOS app, and Audible Google Play memberships — this feature is not available.