What are the requirements for showing financial support for a retirement visa extension in Thailand?

Not so easily doable for those whose embassies don’t issue an “income affidavit” any more.

You need to pay 800.000 THB into your Thai bank account in order to pass the first 12 months in Thailand on a "1-year retirement Extension of Stay Permit" (which is not a "retirement visa")

If your country's embassy in Thailand is among those who stopped issuing income affidavits a long time ago, you are in a Catch22 situation. It is forcing applicants for the "1-year retirement extensions" to collect 12 months of consecutive, month for month, money transfers coming in from abroad, of a minimum of 65.000.- THB.

Only when your Thai bank certifies this with a "one year transfer statement", you will be able to use your income as the financial proof for an application to the next "retirement extension"

Do you need show the 800,000 baht.

Or can you show 12 monthes x 65k. Or show both on non 0 visa?

It also depends on the visa. The requirements for non-immigrant O based on marriage are less (400,000 balance or 45,000 monthly)

If you get monthly deposits every month, your allowed to withdraw?

Has to be a minimum of Thai Baht per month

If you are asking about using the monthly income method to meet the 1 year extension financial requirements then you need to deposit at least 65,000 baht to your bank account each month. You have to show that the money came from outside Thailand (an international transfer).

If you are using the 800,000 baht deposit method then the whole 800,000 must be on deposit in your Thai bank account.

Depends what method you're using as proof of finance.