Can I get a 90-day Non-O visa in Thailand without proof of funds?

From outside Thailand with your home bank.

You need to get the 90 day Non O

In your home country before travelling ...then do the bank account & deposit soonest upon arrival in country ...jmo

Sort of true but you have the sources of these mixed up.

First you get the 90 day VISA from an embassy overseas.. then you can arrive, open a bank account, season the 800k, and apply for the EXTENSION from immigration.

So your sequence isn't wrong, but you need to start it before you arrive.

Just a note, most offices (other than Jomtien) do NOT require you to have the banked money seasoned in your thai bank account for 2 months before you apply for the in country Non-O visa.

Most allow you to apply right after you transfer the money in (as long as you have enough time left on your current stamp which is 15 days at most offices)

Unless I'm mistaken only Jomtien requires the 800K seasoned for the in country Non-O based on retirement.

You need funds if your bank anywhere to get the non-o then you need 800k in your Thai bank for the extension or if your embassy issues a financial certificate you can use that but most don’t issue this anymore

That is unfortunately a 100% misunderstanding of how it works in country. :(

Inside Thailand you need proof of funds to get a 90 day non O visa issued from the immigration office for 2000 baht..

That means if you don't come from a country whose embassy here issues an affidavit of income from abroad notary letter <- which is the only thing accepted by immigrations for proof of funds from abroad, it means you bank the 800k baht in a Thai bank account in your name only. Keep in mind a few offices want to see that the 800k was transferred in from abroad to issue an in country 90 day Non-O visa.

Now with that being said:

Outside Thailand you can apply for a 90 day Non-O visa at a Thai embassy and show proof of funds using your bank account in your country..

Most people get their Non-O visa before they come here, get stamped in for 90 days, open a bank account (which you can do on a 90 day Non-O visa) transfer in the 800k, let it season the 2 months required and then apply for a year extension at the immigration office for 1900 baht.