Can I continue my monthly ฿65,000 deposits for a Thai visa extension if I'm not residing in Thailand?

As long as you met the seasoning requirements for the extension you're on (which you evidently used banked money for) by having the 800K baht in the bank for 3 months after the extension was granted and then never letting the balance go below 400K baht the rest of the year <- BOTH requirements to keep the extension you're on now until you can apply for the next yearly extension using monthly income by transfer of 65K baht a month.

Immigration won't care in the least if you're in or out of thailand, BUT they will wanna see that 65k baht a month transfer, each month, every month for the previous 12 months when you go to apply for the new year extension

I've done that many times. You just have to keep up the monthly payments. That's what immigration is looking for, they don't give a stuff where you are, as long as you're sending the dosh

No issue at all, as long as you are here for you extension and get a re-entry permit