We have in our garden a young apple tree that blooms earlier than most local Malus and needs a pollenizer (another plant to provide compatible pollen). Walking around our neighborhood, we didn’t spot any other blooming Malus. My wife suggested checking iNat, and sure enough there was an observation from last April of a blooming apple tree a very short walk from our house. We walked over there and found just a few active blooms, enough to hand pollinate our little tree. iNat data (including observations of cultivated trees) have so many unexpected little uses!
My wife did it. Got some pollen on the end of a q-tip, carried the q-tip to our tree in a container (so the pollen wouldn’t blow off as we were walking back) and touched the pollen to the stigma of each flower on our tree. It would not be a useful method for a tree with thousands of blooms on it, but for a young tree with just a handful of blooms it works.
I grow pawpaw (Asimina triloba) in SE Texas, well outside of its native range. It also requires cross-pollination for fruit-set. A few years ago when it bloomed for the first time I used iNat to locate a pawpaw tree in a nearby arboretum to go check for flowers. Bingo! FYI, I now have about 20 different pawpaw cultivars I have grafted onto that original plant, so no longer need to go seek out flowers in public places.