For the license to be changed every team member needs to submit a written agreement that he agrees to the change, otherwise their contributions must be removed as they were written under a different license, the only exception is usually permissive licenses such as MIT/BSD 3 clause.

Usually, to rugpull FOSS contributors, companies who maintain FOSS software ask contributors to sign a CLA which waives their rights and lets the control their contributions. Immich isn’t doing any of that, and it will likely remain AGPL forever because changing the license will be a big hassle for them with the amount of contributors.

Hi, I recommend you read the book “Run Your Own Mail Server”. The fact that a book exists for this topic is all the proof you need to not do this decision. But if you absolutely must, this is the way.