the income has to be from overseas not local, you can’t work in Thailand under a retirement system and make an income. That would be a different visas. LTR or investment visa
After you have your 12 month extension of your 90 day non o visa two months later you can do whatever you want with the 800.000 baht but must have 65.000 baht overseas income monthly for 12 months and you can spend all of it if you wish
deposit 800.000 baht for visa extension. The day you extension starts you must pay 65.000 baht into your Thai bank account per month however you can withdraw your 800.000 baht two months as long as you deposit minimum of 65.000 baht per month which you can spend freely
I use wise to transfer my money into my Thai bank account( Bangkok Bank ). Use long term stay in Thailand if you want to go the 65.000 baht per month income route. The first 12 month extension you must use 800.000 baht system. But you must deposit from overseas bank account 65.000 baht per month unbroken for 12 months to use the 65.000 baht system.