Pete Buttigieg did not endorse a candidate in the Michigan Senate primary based on the information surfaced here; the results point instead to his endorsement of Jocelyn Benson in the Michigan governor race.

What this means

The Michigan Senate primary itself was reported as narrowing to Abdul El-Sayed and Haley Stevens after Mallory McMorrow exited the race.
So if you were asking about the Senate primary, there does not appear to be a Buttigieg endorsement in the sources found for that contest.

Related context

Buttigieg has recently been active in Michigan politics more broadly, including public support for Democratic candidates in other races.

That may be why the governor endorsement and the Senate-primary question are getting mixed together. TL;DR: In the Michigan Senate primary, I do not see a Buttigieg endorsement; the clearly documented endorsement is for Jocelyn Benson for governor.