Do I need to show proof of income for my non-OA visa at the 90-day report or during the extension process?

No financial requirements for the 90 days report. You can first go a border bounce before the visa itself expires and get another year off your visa if you update your health insurance.

For extension at the immigration you’ll need to prove 800K baht in a Thai bank account two months prior to the application or get a affidavit letter from your embassy confirming income over 65K baht a month.