ScratchAttach doesn't have this feature(same with scratchclient), and the closest thing it has is getting the number of studios a user is following(not the studios themselves) and that is done by scraping the “Studios I follow (amount)” section of https://scratch.mit.edu/users/{user}/studios_following/. I've been using a regular expression to scrape the studio ids from that page, but I wanted to check if there was a better way, specifically in the form of a dedicated endpoint.

The Scratch API and its endpoints are documented on the Scratch Wiki.

There doesn't appear to be any endpoint on the Scratch API that returns a list of the studios a user is following. The closest match is likely this:
…which returns the current list of projects in the “Projects in Studios I'm Following” section of the front page.

The most straightforward method of getting all the studios a user is following is just to scrape the list on their profile, which is what you've been doing.
Note that the Scratch Team would prefer not to have pages scraped en masse, as it puts strain on the servers and can lead to slowdown.

Scratch137 wrote:

The most straightforward method of getting all the studios a user is following is just to scrape the list on their profile, which is what you've been doing.
Note that the Scratch Team would prefer not to have pages scraped en masse, as it puts strain on the servers and can lead to slowdown.

Interesting, thank you. The page won't be scraped excessively, it's just fetched once.