This begonia has grown very tall and I hesitate to cut any more off of it to propogate.
Unfortunately, they are houseplants in all but zones 10 and 11.
This article will help you to care for the plant indoors:
https://www.gardeningknowhow.com/ornamental/flowers/begonia/angel-wing-begonia-care.htm
This is an indoor plant only
These articles should help:
https://www.gardeningknowhow.com/ornamental/flowers/begonia/angel-wing-begonia-care.htm
https://www.gardeningknowhow.com/ornamental/flowers/begonia/begonia-botrytis-treatment.htm
Previously I left this begonia outside in indirect sunlight in Tennessee. Not enough light inside so took into basement with one window in winter. It dropped all leaves and I cut it back each winter to about 3-4 inches. It always came back in the summer full and tall. I have now moved to Kentucky in a house with a wonderful sun room. I never took it outside this summer because it was happy and thriving inside. I did transplant it to a little larger pot than the one it has been in probably over 10 years. It has never bloomed, wish it would. Seems like it's getting a little lanky and I thought I should prune it back some. Recommendations? It typically is in front of a 6' tall window but xmas tree is there right now.
It should bloom if it gets enough bright, indirect light, humidity, and the proper nutrition. If you aren't fertilizing, try that and see if it blooms. Choose a fertilizer a little higher in phosphorus than nitrogen. You can lightly prune anytime, which also will encourage blooming.
https://www.gardeningknowhow.com/ornamental/flowers/begonia/angel-wing-begonia-care.htm
https://plants.ces.ncsu.edu/plants/begonia-argenteo-guttata/
https://ffl.ifas.ufl.edu/resources/ffl-minute-radio/2021-archive/may-2021/angel-wing-begonias/