Hello fjclw,
You can still share subscriptions, but not purchased apps if you turn off Purchases Sharing. This will prevent other family members from using your payment method. Here is how:
"If you're the family organizer and you want family members to pay for purchases themselves, turn off purchase sharing:
- Go to your Purchase Sharing settings in Settings on your iPhone or iPad or in System Settings on your Mac.
- Turn off purchase sharing:
- On your iPhone or iPad, tap Stop Purchase Sharing.
- On your Mac, click Turn Off, then click Stop Purchase Sharing.
When purchase sharing is turned off, you stop sharing your purchases and lose access to the purchases made by your other family members. However, you can continue to share subscriptions like Apple TV+ and Apple Arcade, but everyone must use their own payment method for purchases.
Learn what to do if you want to leave or disband your family sharing group"
How to share apps and purchases with your family - Apple Support
If you would like to suggest further ideas about sharing purchases but restricting your payment method to other adults within the family, we are always looking for ways to improve our products, so we encourage you to leave feedback here: Product Feedback - Apple
This is the best way to have your voice heard by our designers and engineers.
Take care!