transparent photos dont save

so... im trying to save some silly photos onto my phone, and im using an online software (i think thats what u call it) to make the background transparent. but for some reason my iphone wont allow me to do that anymore?? instead of it being transparent, the background is pure white (its the original color of the background for the photo but still..) i NEVER had this problem before, i have no clue if its the new update or not but its driving me insane. i want to make it into an emoji or sticker for discord or just to have as a photo. again, it wasnt like this before. is........... there any way to fix this????? its super annoying 😞