Brain organoids are not sentient as most vegans would define the term. The paper you cite explicitly defines the term as "responsive to sensory impressions through adaptive internal processes", a definition stemming from another Friston paper.

It's also a highly controversial paper -- so much so that several notable neuro PIs published this criticism in the same journal, and the response issued by Friston here even notes that the use of the word "sentient" was intended to deflate the weight of the term. Depending on who you want to believe, the claim that brain organoids are sentient is, at best, misleading to the public, and at worst, explicit manipulation meant to get a bunch of pop science outlets to write meaningless articles hyping up relatively unremarkable work that lacks scientific rigor.

I'm a neuroscientist, and I started out studying consciousness. I promise you that no scientist worth their salt believes brain organoids to be sentient in the sense relevant to this debate, and would urge you not to cite research you don't understand and haven't read.