includes
“[..]
49. The EDPB does not consider that Article 6(1)(b) would generally be an appropriate lawful basis for processing for the purposes of improving a service or developing new functions within an existing service. In most cases, a user enters into a contract to avail of an existing service. While the possibility of improvements and modifications to a service may routinely be included in contractual terms, such processing usually cannot be regarded as being objectively necessary for the performance of the contract with the user. ”
Also the EDPB again gives special attention to personalisation, saying that where personalisation is not really necessary for the performance of a contract, eg where content personalisation is just used to increase user engagement, data controllers should consider another legal basis
https://edpb.europa.eu/sites/edpb/files/files/file1/edpb_guidelines-art_6-1-b-adopted_after_public_consultation_en.pdf