I will assume that the news about affidavits of monthly income from embassies will be abolished in December and only bank money will be accepted as proof of funds for extension of stays is NOT true. I’ve seen it posted on other pages but no comments here on it to either confirm or deconflict.
TLDR : Answer Summary
The rumors regarding the abolishment of the embassy-issued affidavits of monthly income in December 2018 are unfounded. The UK Embassy altered their rules, but Thai Immigration has not implemented any changes requiring exclusive bank funds. Other forms of proof, such as bank transfers reflecting income above 65,000 THB, may still be accepted. However, the exact requirements remain unclear, and it is advised to consult directly with immigration offices to ensure compliance for stay extensions.