Most of the garden villas seem to have disappeared. and those that are available show up to be booked, but unable to confirm booking?

Please keep in mind that cash availability = points "availability", there are no reliable confirmations of anyone being able to book them on points - be it on the website (no availability after SPG redirection), mobile app (error on last stage) or phone support (they're unable to book right now).

The disappearing availability is probably people booking them with cash on refundable rates and hoping to convert them to points booking once it becomes available later on. This is also what I did, I have 4 different 5-nights refundable cash reservations for the garden villa for different dates (living in Dubai just a 3h flight away so I plan to visit every 3 months for the next year).

Can't see why not? For base category rooms you can always switch between points and cash rates and this is true for any property. For StR Maldives base category room is the garden villa which is confirmed through the availability on Marriott's page (garden villa available = points rate available, otherwise no points availability).

By this logic, once award redemptions are enabled you there should be no issues with changing the rate from cash to points directly in "modify reservation".

In my experience there needs to be availability in the room type you are modifying to modify it.

I think the issue youre going to run into is that there will be no available garden room to book into, since Marriott is no longer capacity controlling awards

Any idea what upgrade costs will look like or what cash rates have been in the past?

The difference between garden villa and OVW is around $200++ so I'd expect something in this range. Once the points bookings are confirmed, I will have my ambassador reach to the hotel and see what they can do.

If you hold existing garden room reservation this shouldn't be an issue? As per the T&S, if a

I have just tried this for the Andaman where I have a cash reservation in 3 days, the hotel is fully sold out but I'm able to change the rate to free nights as well as switch to prepaid or custom rates (gov/AAA).

Oh hmm, maybe I am thinking if you want to shorten or lengthen a stay on the website. Either way, that would be good for you if changing rates isn't an issue.

I also made a refundable cash reservation yesterday for the garden villas. I tried calling in today to have them convert it to a points booking but wasn't successful. I also can't switch it to a point booking online either. Did you have any luck?

This is the million dollar question. Because all availability on the hotel is artificially wiped by all these cash bookings

Doesn't making a owb rezy accomplish the same?

Point bookings go to garden villa now, now OWB

Where did Marriott confirm that there isn't capacity control for the base level room?

I had success calling St. Regis directly at 800-598-1863 and inquiring about availability for Garden Villas and even the OWB award rate with them. Much easier this way! Good luck!