[Honor View 20 Questions & Answers] NekoMichi:
So last night I used OTG-update to install 9.0.1.138 and 9.0.1.140, and unfortunately neither has fixed the problem (even after a full factory reset and setting up as new with all default settings). It seems that both firmwares use the same camera app version (9.0.1.309) so I think that might be why nothing was fixed.

Somehow I was able to access /system/priv-app/HwCamera2/ even without root (read only, no write access). I've dumped the contents of the app and the lib files, and will compare them with files from a working device to see if there are any major differences. It possible that the libraries for AI photography may be missing from my device somehow.

UPDATE 1:

After decompiling the HwCamera2.apk, I found that all the AI scenes are intact. They show the scenes that the AI camera is supposedly capable of detecting:

01/01/2009 00:00 1,548 ic_ai_camera_badminton.xml
01/01/2009 00:00 1,564 ic_ai_camera_bar.xml
01/01/2009 00:00 4,384 ic_ai_camera_baseball.xml
01/01/2009 00:00 2,640 ic_ai_camera_basketball.xml
01/01/2009 00:00 3,396 ic_ai_camera_bee.xml
01/01/2009 00:00 2,060 ic_ai_camera_billiards.xml
01/01/2009 00:00 1,688 ic_ai_camera_bird.xml
01/01/2009 00:00 4,168 ic_ai_camera_bowling.xml
01/01/2009 00:00 1,620 ic_ai_camera_bridge.xml
01/01/2009 00:00 2,872 ic_ai_camera_buildings.xml
01/01/2009 00:00 2,292 ic_ai_camera_butterfly.xml
01/01/2009 00:00 4,496 ic_ai_camera_camel.xml
01/01/2009 00:00 1,720 ic_ai_camera_camera.xml
01/01/2009 00:00 2,284 ic_ai_camera_chess.xml
01/01/2009 00:00 2,368 ic_ai_camera_chinese_knot.xml
01/01/2009 00:00 2,100 ic_ai_camera_deer.xml
01/01/2009 00:00 2,820 ic_ai_camera_dragonfly.xml
01/01/2009 00:00 2,616 ic_ai_camera_electric_vehicle.xml
01/01/2009 00:00 8,536 ic_ai_camera_elephant.xml
01/01/2009 00:00 2,680 ic_ai_camera_european_architecture.xml
01/01/2009 00:00 3,524 ic_ai_camera_fish.xml
01/01/2009 00:00 1,760 ic_ai_camera_football.xml
01/01/2009 00:00 3,880 ic_ai_camera_fu.xml
01/01/2009 00:00 2,828 ic_ai_camera_giraffe.xml
01/01/2009 00:00 3,248 ic_ai_camera_glass.xml
01/01/2009 00:00 2,824 ic_ai_camera_helicopter.xml
01/01/2009 00:00 1,700 ic_ai_camera_high_heeled_shoes.xml
01/01/2009 00:00 2,816 ic_ai_camera_hobbyhorse.xml
01/01/2009 00:00 1,208 ic_ai_camera_indoor.xml
01/01/2009 00:00 2,596 ic_ai_camera_kangaroo.xml
01/01/2009 00:00 1,364 ic_ai_camera_keyboard.xml
01/01/2009 00:00 3,052 ic_ai_camera_ladybird.xml
01/01/2009 00:00 3,572 ic_ai_camera_lakeside_water.xml
01/01/2009 00:00 1,900 ic_ai_camera_liberary.xml
01/01/2009 00:00 8,164 ic_ai_camera_lion.xml
01/01/2009 00:00 1,672 ic_ai_camera_market.xml
01/01/2009 00:00 1,908 ic_ai_camera_mountain.xml
01/01/2009 00:00 1,940 ic_ai_camera_muslim_architecture.xml
01/01/2009 00:00 1,752 ic_ai_camera_pingpong.xml
01/01/2009 00:00 1,276 ic_ai_camera_plane.xml
01/01/2009 00:00 3,364 ic_ai_camera_rabbit.xml
01/01/2009 00:00 1,296 ic_ai_camera_red_envelope.xml
01/01/2009 00:00 2,916 ic_ai_camera_ship.xml
01/01/2009 00:00 3,540 ic_ai_camera_swimming.xml
01/01/2009 00:00 3,864 ic_ai_camera_teddy.xml
01/01/2009 00:00 3,788 ic_ai_camera_tennis.xml
01/01/2009 00:00 2,292 ic_ai_camera_tiger_leopard.xml
01/01/2009 00:00 3,992 ic_ai_camera_tortoise.xml
01/01/2009 00:00 1,236 ic_ai_camera_tower.xml
01/01/2009 00:00 2,148 ic_ai_camera_train.xml
01/01/2009 00:00 2,424 ic_ai_camera_watch.xml
01/01/2009 00:00 3,228 ic_ai_camera_xi.xml
01/01/2009 00:00 2,156 ic_ai_scene_mode_auto.xml
01/01/2009 00:00 3,252 ic_ai_scene_mode_bycicle.xml
01/01/2009 00:00 3,236 ic_ai_scene_mode_cat.xml
01/01/2009 00:00 1,700 ic_ai_scene_mode_clouded.xml
01/01/2009 00:00 3,572 ic_ai_scene_mode_dog.xml
01/01/2009 00:00 5,244 ic_ai_scene_mode_firework.xml
01/01/2009 00:00 2,956 ic_ai_scene_mode_flower.xml
01/01/2009 00:00 2,172 ic_ai_scene_mode_food.xml
01/01/2009 00:00 4,904 ic_ai_scene_mode_group_photo.xml
01/01/2009 00:00 1,664 ic_ai_scene_mode_leaf.xml
01/01/2009 00:00 1,144 ic_ai_scene_mode_night.xml
01/01/2009 00:00 3,296 ic_ai_scene_mode_panda.xml
01/01/2009 00:00 1,908 ic_ai_scene_mode_plant.xml
01/01/2009 00:00 2,132 ic_ai_scene_mode_portrait.xml
01/01/2009 00:00 2,620 ic_ai_scene_mode_room.xml
01/01/2009 00:00 2,396 ic_ai_scene_mode_sand.xml
01/01/2009 00:00 3,136 ic_ai_scene_mode_shop.xml
01/01/2009 00:00 4,164 ic_ai_scene_mode_sky.xml
01/01/2009 00:00 3,596 ic_ai_scene_mode_snow.xml
01/01/2009 00:00 2,612 ic_ai_scene_mode_stage.xml
01/01/2009 00:00 3,348 ic_ai_scene_mode_sunset.xml
01/01/2009 00:00 1,988 ic_ai_scene_mode_text_ad.xml
01/01/2009 00:00 2,584 ic_ai_scene_mode_traditionalbuilding.xml
01/01/2009 00:00 4,492 ic_ai_scene_mode_waterfall.xml

UPDATE 2:

I downgraded to 9.0.1.125 for the hell of it, because it contains version 9.0.0.201 of the camera app. While AI scene enhancements were still broken, the 48MP Ultra Clarity mode was fixed. Another weird thing is that no matter if AI mode is enabled or disabled, whenever I take a photo the thumbnail in the bottom-left will appear AI-enhanced, but switching camera views or opening the Gallery will cause it to revert to non-enhanced. This behaviour is retained even after I re-updated to 9.0.1.140.