"There was a error while preparing to share. Please try again later." - Possible solution

I received the above error while trying to share photos on my new iPhone Xs Max. Many suggested solutions that worked for some and not for others were to power cycle the phone, turn off photo sharing in iCloud, and/or to completely sign out and back into iCloud.

None of those worked for me. What did work, as I'm not currently on WiFi, was to go into Settings -> Photos -> Cellular Data and toggle the switch to on.

I believe what happens is that when you attempt to share photos through the Photos app, it tries to create a public link to your iCloud photo(s) that you wish to share. If those photos aren't uploaded yet, the link cannot be created. If you're on WiFi, you shouldn't have a problem because the default setting is to upload photos to iCloud over WiFi and when the phone has adequate charge. However, if you haven't been on a WiFi for some time, your photos will not have uploaded. Toggling the above setting will ensure your photos are uploaded to iCloud as soon as possible in order to create shareable links. This will, however, use up your data, so be mindful of that.