On 4 July 2019, Bülter joined Bundesliga club 1. FC Union Berlin on a season-long loan, with the club having the option to make the transfer permanent at the end of the season.[5] He made his debut for Union in their first Bundesliga appearance: a 4–0 defeat at home to RB Leipzig.[4] His first goals for Union came in a stunning 3–1 victory at home to Borussia Dortmund: The opening and winning goals in Union's first win in the Bundesliga.[6]
Schalke 04
On 26 June 2021, he agreed to join Schalke 04, newly relegated from the Bundesliga, signing a three-year contract.[7]
TSG Hoffenheim
On 6 July 2023, following Schalke 04 relegation from Bundesliga, he signed with TSG Hoffenheim on a three-year contract.[8]