I used to work in apple support and I’ve combed through all of the information I can find online about this - on my iPhone 7 & XS this was always an available feature/setting and resolved the issue every time I came across it. I have two brand new IPhone 11 Pros and on both devices the setting is missing to toggle on hashtagimages in cellular settings. I’ve reset my network settings and I’ve reset all settings, both did not resolve the issue. Based on what I see in the comments above, if someone has restored their device to factory settings (and not restored a backup, which can restore software errors) and the issue persists this is likely related to iOS 13 and will not be resolved until there’s an update available.