Emoji’s

You do not indicate any other troubleshooting besides resetting the dictionary and removing emoji. I asked about powering the phone off/on. If you already did that, the balance of user troubleshooting is to force restart the iPhone, Force restart iPhone - Apple Support and if that does not help, the last two steps are to create a current backup and then restore the iPhone to that backup, and if that does not work, then restore the device to factory and set it up as new, not using the backup and test the device without adding any additional content to it. Up to you if you wish to go this far. I don't doubt your word, but it seems unusual that it would seem to just happen on the iPhone 8 series.

If you are typing a message, do you see the predictive text just above the keyboard? If you are not seeing predictive text, then you will not see the emoji. This is especially true if the app drawer is open there as well. Just to be sure, if you type a sentence, then tap on the emoji keyboard button, do the words you expect to be replaced by an emoji change color?

So you are saying that besides not seeing an emoji in predictive text, you are not even seeing the text change color to indicate there is an emoji for that particular word? If you go to Settings>General>Keyboards, is the emoji keyboard listed in Keyboards? I'm not aware of any other setting that needs to be turned on or off to get those emoji predictions for you. Have you tried turning the phone off and back on again?

Do you have Predictive Text turned on?