I bought some things in JD.COM, and then a message came, asking for photos of the front and back of my ID card to cope with the customs.

It's true. Third-party sellers in JD.COM can't get the ID data uploaded by you in JD.COM, but the buyer's ID information is required for goods entry and customs clearance, so third parties usually contact users to provide ID information by phone, SMS or door-to-door letter. If you are worried about information leakage, if you have to provide it, copy the front and back of your ID card and write it next to it: it is only used for customs declaration, and you can basically avoid the abuse of your ID card by signing it with an invalid back.