I know this is all kinda "played out" by now. But this article has a nice timeline of all the teams that have been accused and when and by whom and so forth and so on since 2017. Very interesting read and provides a little more perspective to all that was going on then just "these guys cheated", naive way of looking at it.
https://www.cbssports.com/mlb/news/astros-red-sox-sign-stealing-scandal-timeline-everything-we-know-as-mlb-wraps-up-boston-investigation/

Starts with this:

Early 2017

After spending parts of the prior three seasons with the Yankees, veteran Carlos Beltran signs a one-year deal with the Astros for his age-40 season. Early in his tenure, he reportedly tells the Astros that their approach to stealing signs is "behind the times."