[8][9] De Boer moved to Eredivisie club AZ for undisclosed fee on 15 June 2018, signing a four-year contract.
[18][19] He was the team's starter in goal during the 2021–22 season, keeping 12 clean sheets in 41 total appearances,[20] and Roda were knocked out of promotion play-offs by Excelsior on 14 May 2022.
[22] He also lost his place in goal early in the 2023–24 season, with Koen Bucker arriving from Heracles Almelo in mid-August 2023 to immediately become the starter.
[23] On 22 August 2023, Roda JC announced De Boer's departure to recently relegated Danish 1st Division club AaB.
[26] De Boer is a youth international for his country, making his first selection to the Netherlands under-18 on 5 November 2014 under coach Maarten Stekelenburg.