Alice encrypts file using her public key and upload it to decentralised file store (some service). Bob buys access to the file. Is it possible to share decrypted file with Bob without having Alice's key? Decentralised file store doesn't store any private keys, but it knows that Bob has access to the file (e. g. from smart contract).
If there is no limit on the cost of interactions，proxy re-encryption works for you.
Proxy re-encryption (PRE) is a type of public-key encryption (PKE) that allows a proxy entity to transform or re-encrypt data from one public key to another, without having access to the underlying plaintext or private keys.