Cypress Window:Confirm IFrame

[RTJakobs]

Hello, I have been working in Cypress since the beginning of the year and have now encountered the problem that I cannot confirm the deletion confirmation window.
Would anyone here have a solution?
My current code looks like this:

iframeMRechnungRechnungsposition().enter('iframe[src*="InvoiceLine/Edit"]').then(iframeMRechnungRechnungspositionEdit =>{
         iframeMRechnungRechnungspositionEdit().find('button').contains('Löschen').click()
         cy.on('window:confirm', () => true)
      })

Unfortunately Cypress gets stuck on click(), no matter if I insert the cy.on() before or after click()