Learn Farsi: چاشنی که خوب است، ولی این گوشت خیلی شور است و من آن را نمی‌خورم. - The seasoning is good, but this meat is very salty and I don't eat it.

In this lesson's structure, که acts as a topicalization marker used for concession. By putting که right after the noun چاشنی (seasoning), the speaker isolates it to say, As for the seasoning, it is good, but... This sets up a contrast, which is immediately followed by ولی (but) to introduce the actual problem with the meat.

Does چاشنی refer specifically to salt, or does it mean something else here?

چاشنی is a broad term for seasoning, flavoring, or a condiment. It refers to the overall spice mix, marinade, or sauce used to flavor the food. Since the meat is described as شور (salty), the speaker is contrasting the pleasant flavor of the marinade with the heavy-handed use of salt on the meat itself.

Could I drop آن را and just say من نمی‌خورم?

You could, but including آن را (the pronoun for it plus the specific direct object marker) makes the sentence much more precise. It ensures the listener knows you are refusing to eat that specific meat, rather than making a general statement about not eating. In very casual speech, it is actually more common to drop the subject من and keep آن را نمی‌خورم.

The English translation says I don't eat it, but wouldn't an English speaker say I'm not going to eat it in this situation? Why use نمی‌خورم?

In Farsi, the present tense formed with the می prefix (here negative: نمی‌خورم) is very versatile. Aside from meaning a general habit, it is frequently used for immediate future intentions or refusals. So here, it perfectly captures the feeling of I am not going to eat this right now without needing a separate future tense structure.