The technicality of usage rights is irrelevant, the developer is asking you to pay a set price that they've set as the total they would like to be reimbursed for providing the development service. That's not a contribution, that's a purchase. They're generous people though, so they won't restrict your use of the software if you choose not to pay.

Maybe you make donations to FOSS developers regularly. Unfortunately, I did not in the past. While I always intended to, it just slipped through the cracks. After running in to FUTO and the software they sponsor, I've been motivated to donate to or purchase much of the free software I'm using, and it's entirely because of the way they approach their relationship with the user.

If you feel like that's a dark pattern, or that your payment would only be purchasing an empty NFT, then I guess that's your choice. But purchasing FOSS applications provides an incredibly important line of support to developers who stem the tide of surveillance capitalism and the digital abuse that big tech has filled our world with. Call it a donation, contribution or purchase price. In any case you are exchanging value for something that has made your life better and supporting the person who made that possible.

Maybe it would help to view the cost of Immich as purchasing a ethics NFT. Sure, you have no observable difference in the material world, but you as a person have affirmed your ethical values through reciprocal action with someone who shares those values 😉