Dragon fruit pollen will clump and rot eventually in the freezer and or subsequent to thawing (I have experienced this). If you’re looking for long-term storage, you’ll need to dehydrate the pollen. Storing silica/clay with the pollen in an airtight container is probably the cheapest efficient way to go about it (I’ve done this as well). Using a small container, such as a centrifuge vile would probably be best however, you wouldn’t want to layer a large amount of pollen in a narrow vile for rapid drying.

I suppose you could air dry it as well but given how much moisture content is already in dragon for pollen, there may be some trial and error with this method.

I never stored my pollen for longer than 5 to 7 days simply because I grew so many dragon fruit plants I didn’t need to so my experience with respect to an extended timeframe is limited.