I am so confused by this and feel horribly stupid if it's something I overlooked. But I didn't think I needed it since the top bullet point reads "The spouse or civil partner of someone settled in the UK"
My husband is in the US with me, not settled in the UK. Am I just supposed to pretend that he's in the UK?
Ah, it's a little confusing, but 'settled in the UK' means he has the legal right to live in the UK without restriction, i.e. he is either a UK citizen or a UK permanent resident. It doesn't matter if he currently lives overseas, he is still considered 'settled in the UK'.
The online application is only actually a small part of the whole application form - it's just a generic form about your personal circumstances and is the same for almost all visa types.
The VAF4a Appendix 2 is the main part of the application form, and it covers how you meet each requirement of the spousal visa: the relationship, accommodation and financial requirements.
Without Appendix 2, your application is not complete and cannot be processed. They've been good about contacting applicants to ask for it recently - they could have just refused the visa outright due to it being an incomplete application.