@Stemy
I had the same issue. I rescued by bricked phone by installing android 10 (accroding to https://support.fairphone.com/hc/en-us/articles/18896094650513-Install-Fairphone-OS-manually#01HB8ZZ1BMMQNSNMFT3YXDBXA0) and afterwards I installed ubuntu touch via the UBports Snap again.

The error still appeared after the installation but now my phone boots without any issue.