The highly rated Poland international came through the youth ranks at Poznan, before making his first team debut in April 2018, then spending a season on loan at Polish second division side Odra Opole. 

He returned to Poznan for the 2019/20 campaign and was a mainstay in the side as they finished second in Ekstraklasa (the Polish top-flight), qualifying for the Europa League.

A call-up to the Poland senior team followed, with the 22-year-old making his debut for his country in September 2020.

He signed for Albion a month later and was immediately loaned back to Poznan, with the club's place in the Europa League seen as a good way of Moder continuing his development.

He was recalled from his loan in Poland in December 2020.

After making his Premier League debut as a late substitute at West Brom in February 2021, he made his first league start for Albion the following month in a 3-0 victory against Newcastle United.

Moder helped his country to qualification for the World Cup in Qatar in April 2022, but ruptured his ACL later that week in a 0-0 draw against Norwich City, bringing his season to an early and disappointing end. The injury would see him miss the entirety of the 2022/23 campaign.