Hi Matteo,
Thank you for the confirmation.
At the moment, you would not be able to set selective optimization for Search and Display campaigns in the API because it was never formally supported for the said campaign types.
However, there is now a way to set conversions for a campaign. We just released v9 of the Google Ads API (
https://ads-developers.googleblog.com/2021/11/announcing-v9-of-google-ads-api.html). In the release, there is a concept called Conversion Goals (
https://developers.google.com/google-ads/api/docs/conversions/goals/overview) where you can set custom goals for your campaign. You would need to upgrade to this version to use the feature.
In the meantime, our team is currently looking into turning on selective optimization for Display and Search for the few people who were using it before. You can also alternatively look at v9 as an option as it will be the primary way to set custom goals going forward, and you'll need to move to that way in the future anyway.
Best regards,