I see it has been mentioned but here is an answer and one way to get past this for now: View the photo that you want to send on your iphone and take a "screenshot" of the picture. Save that picture to your photos. This will create a photo in the format of PNG or JPEG which can then be sent to an android user. You will see that without doing this, most likely your photos are in a format of HEIFF which is what causes the incompatibility issue
I have successfully sent pictures using the above to 2 recipients that I had "delivery failures" previously. I hope I have finally got past this. FYI - iphone 14 max pro. Pictures were sent over wifi since I was in my house but I didn't use airplane mode or turn off cellular.